# Warmy Blog --- ## Pages - [404: You got lost, but your emails still can find inbox](https://www.warmy.io/blog/404-you-got-lost/): The page is not exist, and you got lost. Still, you can help your emails to find the primary inbox of your recipients with Warmy.io. - [Home](https://www.warmy.io/blog/): Explore Warmy.io's blog for expert tips on boosting email deliverability with our AI-powered warm-up tool and best practices for inbox success. --- --- ## Posts - [The Fastest Path to Yahoo Inboxes: Analyzing SMTP Providers for Optimal Delivery](https://www.warmy.io/blog/the-fastest-path-to-yahoo-inboxes/): The Warmy Research Team conducted an experiment to uncover which among different SMTP providers result in a faster delivery to Yahoo inboxes. - [The Email Deliverability Roadmap: Getting More Opens, Clicks, and Sales](https://www.warmy.io/blog/email-deliverability-roadmap/): This email deliverability roadmap is designed to help senders optimize each stage of the email marketing journey. - [Don’t Let Your Pixels Hide: The Impact of Tracking Links and Images on Gmail and Google Workspace Deliverability](https://www.warmy.io/blog/impact-of-tracking-links-deliverability/): Warmy tested the impact of tracking links and tracking pixels on deliverability, as well as the impact of the "Show Image" prompt in tracking. - [Scaling Email Outreach: Here’s How to Calculate Your Ideal Mailbox Setup](https://www.warmy.io/blog/scaling-outreach-ideal-mailbox-setup/): When it comes to scaling email outreach, you need to calculate your ideal mailbox setup to avoid throttling and higher bounce rates. - [The Beginner’s Guide to Running an Email Deliverability Test Like a Pro](https://www.warmy.io/blog/beginners-email-deliverability-test/): Learn how to do a basic email deliverability test, and explore the metrics you need to track and monitor for cold outreach success. - [Email Warmup Tools and Strategies for Cold Outreach](https://www.warmy.io/blog/email-warmup-strategy-and-tools/): In this blog, we’re going to walk you through how to create an advanced email warmup strategy, designed specifically for cold outreach campaigns. - [Automate Like a Pro: How Cold Email Sequencers Boost ROI](https://www.warmy.io/blog/how-cold-email-sequencers-boost-roi/): Learn how cold email sequencers contribute to your ROI and how you can execute them with Warmy's tools. - [Best Email Deliverability Tools for Cold Emailing](https://www.warmy.io/blog/best-deliverability-tools-cold-emails/): Not all tools are created equal. Learn about the best email deliverability tools you can utilize to maximize your cold emailing and outreach efforts. - [Everything You Need to Know About Email Deliverability—Explained for Non-Techies](https://www.warmy.io/blog/email-deliverability-for-non-techies/): Email deliverability is essential for email marketing but it's a complicated concept for non-technical users. Here, we explain it in simple terms. - [Cold Email Sequences: What They Are and How to Create One That Converts](https://www.warmy.io/blog/cold-email-sequences-what-they-are-and-how-to-create-one-that-converts/): Cold email is an integral part of any sales and marketing strategy. Learn how to execute cold email sequences that bring in results. - [Why Cold Email Sequencers Are the Secret to Successful Outreach](https://www.warmy.io/blog/cold-email-sequencers-for-outreach/): We’re going to seriously unpack cold email sequencers—what they are and why they’re insanely important when it comes to your outreach. - [Mailbox Calculator Explained: What It Is and Why Email Marketers Use It](https://www.warmy.io/blog/mailbox-calculator-explained-what-it-is-and-why-email-marketers-use-it/): A mailbox calculator helps email marketers optimize their sending volume while protecting their sender reputation. Learn more here. - [Email Deliverability Demystified: A Simple Guide for Startups & Solo Founders](https://www.warmy.io/blog/email-deliverability-demystified-a-simple-guide-for-startups-solo-founders/): For startups and solo founders who wear multiple hats, email deliverability issues must be a priority before they cause long-term damage. - [How Many Mailboxes Do You Really Need for Email Outreach?](https://www.warmy.io/blog/how-many-mailboxes-do-you-really-need-for-email-outreach/): Learn how many mailboxes you should use for your cold email outreach strategy to succeed. Plus, see how a Mailbox Calculator can help. - [Is Your Cold Email Template Getting You Marked as Spam?](https://www.warmy.io/blog/is-your-cold-email-template-getting-you-marked-as-spam/): Don’t let a flawed cold email template ruin your outreach. Use Warmy.io’s built-in deliverability tools before launching your next campaign. - [Why Your Cold Email Strategy Needs a Mailbox Calculator (and How to Use One)](https://www.warmy.io/blog/why-your-cold-email-strategy-needs-a-mailbox-calculator-and-how-to-use-one/): Learn why mailbox calculators are important for cold email strategies, how they work, and how to use them along with other warmup tools. - [From Spam Folder to Inbox: Mastering Email Deliverability Basics](https://www.warmy.io/blog/from-spam-folder-to-inbox-mastering-email-deliverability-basics/): Learn all about email deliverability basics that will help you avoid spam folder and improve email deliverability. - [Build a Signature That Works: What Every Outreach Email Should Include](https://www.warmy.io/blog/build-a-signature-that-works-for-email-outreach/): Email signature deliverability contributes to the success of your email outreach. Learn how you can craft signatures that avoid spam filters. - [Signature Showdown: Crafting the Perfect Email Signature for Maximum Deliverability](https://www.warmy.io/blog/signature-showdown-crafting-the-perfect-email-signature/): Warmy tested six different email signature templates across various providers to discover how signatures affect deliverability across ESPs. - [Cold Email Campaigns vs. Cold Email Sequences What’s the Difference](https://www.warmy.io/blog/cold-email-campaigns-vs-cold-email-sequences-whats-the-difference/): Cold outreach through email marketing is still a cornerstone of sales and marketing in 2025. With an ROI of $36 per $1 spent - [Signature Builder Tools: What They Are & How to Use Them to Look More Credible](https://www.warmy.io/blog/signature-builder-tools-what-they-are-how-to-use-them/): Explore how signature builder tools can help improve your deliverability and overall success of your cold email outreach. - [The Perfect Cold Email Schedule Timing, Frequency & Follow-Ups](https://www.warmy.io/blog/the-perfect-cold-email-schedule-timing-frequency-follow-ups/): Timing is everything when it comes to cold email outreach. An email can be perfectly composed but it won’t be effective - [Why Your Email Signature Might Be Hurting Your Deliverability](https://www.warmy.io/blog/why-your-email-signature-might-be-hurting-your-deliverability/): Email deliverability can be the difference between success or failure of your outreach. You could be doing everything perfectly. - [Email Signature Best Practices for Cold Outreach Campaigns](https://www.warmy.io/blog/email-signature-best-practices-for-cold-outreach-campaigns/): When it comes to cold email outreach, the devil is literally in the details. From the subject line to the body copy - [Email Deliverability Testing 101: Tools, Metrics & What You Should Be Looking For](https://www.warmy.io/blog/email-deliverability-testing-101-tools-metrics-what-you-should-be-looking-for/): The success of your email marketing efforts depends a great deal on your email deliverability. No matter how strong your message is - [Write Better Cold Emails — Using a Template Checker to Boost Deliverability](https://www.warmy.io/blog/write-better-cold-emails-using-a-template-checker-to-boost-deliverability/): When it comes to cold email outreach, the name of the game is deliverability. It doesn't matter how compelling your message - [Mailbox Math How to Optimize Sending Volume Without Hurting Deliverability](https://www.warmy.io/blog/mailbox-math-how-to-optimize-sending-volume-without-hurting-deliverability/): The truth is, most of the people that get into marketing are not big math lovers. Numbers, formulas, and equations can feel like a language - [The Anatomy of a High-Performing Cold Email](https://www.warmy.io/blog/the-anatomy-of-a-high-performing-cold-email/): Learning how to implement cold email outreach is imperative for any person in marketing, sales, or any entrepreneur who wants to grow - [How to Spot Deliverability Issues Before They Tank Your Campaign](https://www.warmy.io/blog/how-to-spot-deliverability-issues-before-they-tank-your-campaign/): Email deliverability—one of the most critical factors in the success of email marketing campaigns, yet often the hardest to maintain - [The Power of a Great Email Signature in Building Trust with Cold Leads](https://www.warmy.io/blog/the-power-of-a-great-email-signature-in-building-trust-with-cold-leads/): An email signature is not just a line with contact info at the end of your cold email, is so much more. It’s part of the first-hand impression - [Set Up DMARC in 5 Minutes with a Generator](https://www.warmy.io/blog/set-up-dmarc-in-5-minutes-with-a-generator/): If your means of business communications includes emails, it is important to secure your domain from bad actors. - [Words That Trigger Spam Filters (And How to Fix Them with a Template Checker)](https://www.warmy.io/blog/words-that-trigger-spam-filters-and-how-to-fix-them-with-a-template-checker/): Every marketer wants to know their email campaign is well-received, lands straight in the inbox, and gets the recipients to take action. - [How to Use an SPF Generator to Protect Your Domain and Improve Inboxing](https://www.warmy.io/blog/how-to-use-an-spf-generator-to-protect-your-domain-and-improve-inboxing/): Email is one of the most powerful tools for communication. However spam, phishing, and spoofing continue to be an ongoing risk - [Don’t Let Your Emails Get Spoofed: How a DMARC Generator Helps](https://www.warmy.io/blog/dont-let-your-emails-get-spoofed-how-a-dmarc-generator-helps/): Email spoofing is possibly the biggest danger in email marketing. Not only does it put recipients at risk, it can also destroy a brand. - [Cracking the Inbox Code: What Speeds Up Outlook Delivery from Different SMTP Providers?](https://www.warmy.io/blog/cracking-the-inbox-code-what-speeds-up-outlook-delivery-from-different-smtp-providers/): If you’ve ever wondered why some domains warm up faster than others, you’re not alone. For marketers and businesses, speed to inbox - [How a Template Checker Can Save Your Email Campaigns](https://www.warmy.io/blog/how-a-template-checker-can-save-your-email-campaigns/): We’re certain you’ve experienced this scenario too many times before. You’re looking forward to checking the open rates - [SPF, DKIM, and DMARC: What They Are and Why You Should Care](https://www.warmy.io/blog/spf-dkim-and-dmarc-what-they-are-and-why-you-should-care/): It's that time of day where you open your email marketing platform's dashboard to check the numbers. Your open rates are unexpectedly low. - [5 Warning Signs Your Email Deliverability Is Suffering](https://www.warmy.io/blog/5-warning-signs-your-email-deliverability-is-suffering/): You've set up your workflows and sequences to be as detailed as possible—taking into account all possible behaviors - [Why Your Emails Aren’t Reaching Inboxes](https://www.warmy.io/blog/why-your-emails-arent-reaching-inboxes/): The subject is attention-getting, the design is beautiful and your offer…? Spot on. You hit send, you wait … and then comes the letdown - [Best Email Warm-Up Tools for Gmail](https://www.warmy.io/blog/best-email-warm-up-tools-for-gmail/): Email is without a doubt an insanely effective tool when it comes to marketing your business. Among email providers - [Email Deliverability Benchmarks for Recruitment & HR](https://www.warmy.io/blog/email-deliverability-benchmarks-for-recruitment-hr/): Email is a critical communication tool for recruitment and HR teams—whether you’re contacting candidates, following up on job - [How Long Does It Take to Warm Up an Email Domain for Cybersecurity](https://www.warmy.io/blog/how-long-does-it-take-to-warm-up-an-email-domain-for-cybersecurity/): Cybersecurity companies work in an industry where trust, security, and compliance are everything. Emails must not only land in the inbox! - [Best Email Marketing Platforms for SaaS Companies](https://www.warmy.io/blog/best-email-marketing-platforms-for-saas-companies/): Email marketing still reigns as one of the most powerful channels for nurturing prospects, leads, and customers for SaaS companies. - [How Long Does It Take to Warm Up an Email Domain for Fintech Companies](https://www.warmy.io/blog/how-long-does-it-take-to-warm-up-an-email-domain-for-fintech-companies/): Email is essential for fintech businesses when it comes to communicating with prospects, customers, and partners. - [Email Deliverability Benchmarks for Marketing Agencies](https://www.warmy.io/blog/email-deliverability-benchmarks-for-marketing-agencies/): For marketing agencies sending email campaigns at volume, there are key metrics that matter, when it comes to understanding deliverability - [Improve Email Deliverability in Outlook](https://www.warmy.io/blog/improve-email-deliverability-in-outlook/): But with Outlook’s aggressive spam filters and intricate security precautions, getting your emails delivered could be quite difficult. - [Top Email Marketing Tips for SaaS Companies](https://www.warmy.io/blog/top-email-marketing-tips-for-saas-companies/): In the SaaS landscape, success lies in nurturing leads and retaining customers. After all, the subscription business industry - [How Long Does It Take to Warm Up an Email Domain for Marketing Agencies](https://www.warmy.io/blog/how-long-does-it-take-to-warm-up-an-email-domain-for-marketing-agencies/): When it comes to marketing agencies, email is not just a tool for communication, it’s the horse that pulls client email outreach - [Top Email Marketing Tips for Ecommerce Platforms](https://www.warmy.io/blog/top-email-marketing-tips-for-ecommerce-platforms/): In the fast-moving world of ecommerce, competition can be tough. With the market revenue expected to reach US 4.32 trillion in 2025 - [How to Increase Email Deliverability in the UK Market](https://www.warmy.io/blog/how-to-increase-email-deliverability-in-the-uk-market/): In the UK alone, 8.3 billion (as of April 2024) emails are sent each day, opening up vast potential for business growth. - [Improve Email Deliverability in Gmail](https://www.warmy.io/blog/improve-email-deliverability-in-gmail/): Gmail's spam abyss is much like the internet's black hole—where your carefully crafted emails vanish. Well, you're not alone. - [Email Marketing Compliance Checklist for US Market](https://www.warmy.io/blog/email-marketing-compliance-checklist-for-us-market/): With a $36 return on every $1 spent, email marketing is a valuable tool for businesses to interact with customers and increase sales - [Free vs Paid Email Warm-Up Tools: Which Is Best?](https://www.warmy.io/blog/free-vs-paid-email-warm-up-tools-which-is-best/): When it comes to email outreach, getting your emails into the primary inbox—not spam or promotions—is everything - [How Long Does It Take to Warm Up an Email Domain for SaaS Companies?](https://www.warmy.io/blog/how-long-does-it-take-to-warm-up-an-email-domain-for-saas-companies/): If you're sending cold emails for your SaaS company, you probably spend a lot of time crafting really great copy - [How to Increase Email Deliverability in the US Market](https://www.warmy.io/blog/how-to-increase-email-deliverability-in-the-us-market/): Learning the intricacies of email deliverability to US contacts is a must for global marketing teams, SDRs, and agencies - [Why Your Emails Land in Spam: Deliverability Tips](https://www.warmy.io/blog/why-your-emails-land-in-spam-deliverability-tips/): Emails are an integral part of digital marketing. However, even the most beautifully-written emails end up in the spam holder - [Email Warm-Up Checklist for New Domains in 2025](https://www.warmy.io/blog/email-warm-up-checklist-for-new-domains-in-2025/): In 2025, email service providers ESPs have leveled up when it comes to security and strict spam filtering mechanisms. - [Thread or Dread: GSuite vs. MS365 in Follow-Up Deliverability](https://www.warmy.io/blog/thread-or-dread-gsuite-vs-ms365-in-follow-up-deliverability/): In the world of email deliverability, most senders obsess over one moment: the first send. Will it land in the inbox or spiral into spam? - [It’s Time to Bounce Back: ESP-Specific Strategies That Actually Work](https://www.warmy.io/blog/its-time-to-bounce-back-esp-specific-strategies-that-actually-work/): Whether you are running cold outreach, nurturing leads, or sending out transactional updates, bounced emails are an annoyance - [Mastering Global Email Deliverability in 2024–2025](https://www.warmy.io/blog/mastering-global-email-deliverability-in-2024-2025/): As businesses expand their reach beyond borders, making sure that emails are received and land in people's inboxes becomes vital - [Are Blacklists Killing Your Emails? A Deep Dive into How They Influence Email Providers](https://www.warmy.io/blog/are-blacklists-killing-your-emails-a-deep-dive-into-how-they-influence-email-providers/): Discover how email blacklists affect your deliverability and learn how to avoid getting flagged by major email providers. - [How to Avoid Email Blocks: Lessons from MS365’s Deliverability Research](https://www.warmy.io/blog/how-to-avoid-email-blocks-lessons-from-ms365s-deliverability-research/): Email deliverability—crucial yet often elusive goal for businesses aiming to connect with their audience. But there’s a harsh reality - [The Email Deliverability Playbook: 5 Key Trends That Will Define Inbox Success in 2025](https://www.warmy.io/blog/the-email-deliverability-playbook-5-key-trends-that-will-define-inbox-success-in-2025/): Welcome to the new email landscape where email deliverability has never been more important. With inbox providers tightening their rules - [SMTP Error 451 4.4.2 – Bad Connection to Remote Mail Server: Causes & Fixes](https://www.warmy.io/blog/smtp-error-451-4-4-2-bad-connection-to-remote-mail-server-causes-fixes/): In this guide, we’ll walk you through what causes SMTP Error 451 4.4.2, how to troubleshoot and fix it - [SMTP Error 502 5.5.1 – Command Not Implemented: How to Fix It](https://www.warmy.io/blog/smtp-error-502-5-5-1-command-not-implemented-how-to-fix-it/): If you’ve ever had to deal with the dreaded SMTP Error 502 5.5.1 – Command Not Implemented that occurs while attempting to send an email - [SMTP Error 421 4.3.0 – Temporary Mail Server Error Causes & Fixes](https://www.warmy.io/blog/smtp-error-421-4-3-0-temporary-mail-server-error-causes-fixes/): In this guide, we’re going to explain exactly what SMTP Error 421 4.3.0 means, why it happens, and how you can resolve it quickly. - [Mastering Email Deliverability: The Modern Guide to Authentication and Inbox Warm-Up](https://www.warmy.io/blog/mastering-email-deliverability-the-modern-guide-to-authentication-and-inbox-warm-up/): In the world of emails, getting your message seen is just as important as crafting the perfect copy. - [SMTP Error 555 5.5.2 – Syntax Error: Causes & Fixes](https://www.warmy.io/blog/smtp-error-555-5-5-2-syntax-error-causes-fixes/): It can feel like hitting a wall when you run into SMTP Error 555 5.5.2—and everything seems to be configured correctly. - [SMTP Error 421 4.7.27 – Connection Rate Limited: Causes & Solutions](https://www.warmy.io/blog/smtp-error-421-4-7-27-connection-rate-limited-causes-solutions/): If SMTP Error 421 4.7.27 lands in your lap, it’s a warning sign—a gentle reminder from the email gods to stop - [Understanding ESP Blocks: Causes, Types, and Prevention](https://www.warmy.io/blog/understanding-esp-blocks-causes-types-and-prevention/): This report is more than just an overview. It is carefully tailored to support Warmy users in maximizing their email deliverability - [SMTP Error 421 4.7.30 – Temporary Ban Due to Abuse Detection How to Fix It](https://www.warmy.io/blog/smtp-error-421-4-7-30-temporary-ban-due-to-abuse-detection-how-to-fix-it/): You’ve crafted the perfect email campaign, targeted your audience, and hit “send.” But then, an unsettling notification appears in your inbox - [SMTP Error 554 5.4.6 – Too Many Hops: How to Fix It](https://www.warmy.io/blog/smtp-error-554-5-4-6-too-many-hops-how-to-fix-it/): SMTP Error 554 5.4.6 "Too Many hops" is one of the most common errors faced by email administrators. - [SMTP Error 550 5.2.1 – Mailbox Unavailable: Causes & Fixes](https://www.warmy.io/blog/smtp-error-550-5-2-1-mailbox-unavailable-causes-fixes/): The number of emails sent and received worldwide per day is predicted to reach 408.2 billion by 2027 - [SMTP Error 552 5.2.2 – Mailbox Full: How to Fix & Prevent It](https://www.warmy.io/blog/smtp-error-552-5-2-2-mailbox-full-how-to-fix-prevent-it/): SMTP Error 552 5.2.2 is an error that indicates that the recipient’s mailbox has reached its storage limit. - [Outlook Seed Lists & MS365 Deliverability: The Battle Between New and Established Lists](https://www.warmy.io/blog/outlook-seed-lists-ms365-deliverability-the-battle-between-new-and-established-lists/): Improve email deliverability in MS365! Learn how to avoid spam filters, boost inbox placement, and maximize engagement. - [SMTP Error 554 5.6.0 – Message Content Rejected: How to Fix It](https://www.warmy.io/blog/smtp-error-554-5-6-0-message-content-rejected-how-to-fix-it/): SMTP Error 554 5.6.0 is one that the email sender never wants to encounter. That means an email was rejected because of content issues. - [SMTP Error 550 5.5.3 – Too Many Recipients: How to Fix & Avoid It](https://www.warmy.io/blog/smtp-error-550-5-5-3-too-many-recipients-how-to-fix-avoid-it/): SMTP Error 550 5.5.3 means your email provider rejected your email because there were too many recipients. - [SMTP Error 421 4.7.28 – IP Temporarily Blocked: Causes & How to Fix It](https://www.warmy.io/blog/smtp-error-421-4-7-28-ip-temporarily-blocked-causes-how-to-fix-it/): If your emails are suddenly bouncing back with SMTP Error 421 4.7.28, your IP address has been temporarily blocked - [SMTP vs. ESMTP: Key Differences and Why They Matter for Email Delivery](https://www.warmy.io/blog/smtp-vs-esmtp-key-differences-and-why-they-matter-for-email-delivery/): Email is a top communication tool, but behind the scenes, strict rules guide its journey to ensure safe delivery across the internet. - [SMTP Error 451 4.7.23 – Email Blocked Due to SPF Failure: How to Fix It](https://www.warmy.io/blog/smtp-error-451-4-7-23-email-blocked-due-to-spf-failure-how-to-fix-it/): Authentication failures resulting in blocked or bounced emails are some of the most frustrating problems that senders have to deal with - [SMTP Error 421 4.7.29 – Suspicious Activity Detected: Fixing Email Sending Issues](https://www.warmy.io/blog/smtp-error-421-4-7-29-suspicious-activity-detected-fixing-email-sending-issues/): Picture this: You’re about to send out an important email campaign, targeting thousands of potential customers or partners. - [SMTP Error 451 4.5.0 – Mailbox Unavailable: How to Fix It](https://www.warmy.io/blog/smtp-error-451-4-5-0-mailbox-unavailable-how-to-fix-it/): For email senders, one of the most frustrating things that can happen is messages not getting to the intended recipients. - [Email Engagement How Seed List Helps Improve Open & Click Rates](https://www.warmy.io/blog/email-engagement-how-seed-list-helps-improve-open-click-rates/): It is easy for Internet Service Providers (ISPs) — such as Gmail, Yahoo, and Outlook to categorize your messages as spam - [Email Warmup Alternatives: When Traditional Warmup Isn’t Enough](https://www.warmy.io/blog/email-warmup-alternatives-when-traditional-warmup-isnt-enough/): Cold email outreach is a powerful weapon for businesses, but it only works if you can ensure email deliverability - [Inbox vs. Spam: How DNS Configuration & Email Templates Affect Your Email Success](https://www.warmy.io/blog/inbox-vs-spam-how-dns-configuration-email-templates-affect-your-email-success/): One of the essential factors for any successful email outreach strategy is email deliverability. - [SMTP Error 421 4.7.0 – Temporary Email Rejection: Causes & Fixes](https://www.warmy.io/blog/smtp-error-421-4-7-0-temporary-email-rejection-causes-fixes/): If you are running email marketing campaigns or doing customer outreach, email deliverability can be a best friend or worst enemy. - [Google Postmaster Issues Fixing Bad IP & Domain Reputation](https://www.warmy.io/blog/google-postmaster-issues-fixing-bad-ip-domain-reputation/): A decline in the sender’s IP or domain reputation is most likely the reason why their emails are going to junk or spam - [SPF Alignment Issues: Causes, Fixes & Best Practices for Better Email Authentication](https://www.warmy.io/blog/spf-alignment-issues-causes-fixes-best-practices-for-better-email-authentication/): Crazy to think what happens when you hit "Send"—your email races through networks, security checks & spam filters in seconds! - [SMTP Error 421 4.4.3 – Routing Server Failure Causes & Solutions](https://www.warmy.io/blog/smtp-error-421-4-4-3-routing-server-failure-causes-solutions/): Error 421 is likely the cause of heavy load or maintenance from the server’s side, variant 4.4.3 means that there may be some misconfiguration - [SMTP Error 421 4.7.26 – Email Rate Limit Exceeded: Causes & Fixes](https://www.warmy.io/blog/smtp-error-421-4-7-26-email-rate-limit-exceeded-causes-fixes/): Sending limits and anti-spam measures are being imposed by Internet Service Providers (ISPs) and Email Service Providers - [SMTP STARTTLS Errors Causes, Fixes & How to Ensure Secure Email Communication](https://www.warmy.io/blog/smtp-starttls-errors-causes-fixes-how-to-ensure-secure-email-communication/): eing exposed to email security risks is something we all want to avoid; security risks such as man-in-the-middle (MITM) attacks - [SMTP Error 451 4.7.26 – Email Blocked Due to Poor Domain Reputation](https://www.warmy.io/blog/smtp-error-451-4-7-26-email-blocked-due-to-poor-domain-reputation/): Email deliverability is essential to any effective email marketing or transactional email plan. Receiving SMTP Error 451 4.7.26 - [SMTP Error 451 4.7.24 – DMARC Policy Failure: Causes & Solutions](https://www.warmy.io/blog/smtp-error-451-4-7-24-dmarc-policy-failure-causes-solutions/): Now more than ever, email security is vital. Cybercriminals leverage email vulnerabilities to impersonate businesses - [The Science and Process of Warming Up Newly Created Email Domains](https://www.warmy.io/blog/the-science-and-process-of-warming-up-newly-created-email-domains/): One of the many reasons why your emails are probably going to spam or junk is because you have a new email or domain - [Fixing SMTP Error 421 4.4.2 – Bad Connection What You Need to Know](https://www.warmy.io/blog/fixing-smtp-error-421-4-4-2-bad-connection-what-you-need-to-know/): The most difficult part of creating email content and developing email marketing strategies is actually crafting the campaign right? - [How to Solve SMTP Error 421 4.4.5 – Server Congestion Issues](https://www.warmy.io/blog/how-to-solve-smtp-error-421-4-4-5-server-congestion-issues/): Server congestion, or SMTP error 421 4.4.5, happens when an email server is overloaded with incoming or outgoing email requests. - [SMTP Connection Encryption: The Key to Secure & Reliable Email Delivery](https://www.warmy.io/blog/smtp-connection-encryption-the-key-to-secure-reliable-email-delivery/): One of the top channels of communication for businesses is email, which unfortunately makes it one of the prime targets of cyberthreats like phishing - [SMTP Error 421 4.3.2 – Service Shutting Down Causes & How to Fix It](https://www.warmy.io/blog/smtp-error-421-4-3-2-service-shutting-down-causes-how-to-fix-it/): One of these temporary errors is the SMTP error 421 4.3.2 (Service Shutting Down), an incident where a mail server unexpectedly closes down. - [How SMTP AUTH Mechanisms Affect Email Deliverability and Security](https://www.warmy.io/blog/how-smtp-auth-mechanisms-affect-email-deliverability-and-security/): Having Warmy as your overall email deliverability system can provide you with the capability to configure your SMTP setting - [SMTP AUTH Mechanisms Explained Choosing the Right Authentication for Secure Email Sending](https://www.warmy.io/blog/smtp-auth-mechanisms-explained-choosing-the-right-authentication-for-secure-email-sending/): SMTP AUTH mechanisms explained: Learn how to choose the right authentication method for secure and reliable email sending. - [Fixing Reverse DNS Lookup Failures Best Practices for Email Server Configuration](https://www.warmy.io/blog/fixing-reverse-dns-lookup-failures-best-practices-for-email-server-configuration/): Email is an instrumental communication tool that finds its advantages in areas such as marketing, customer support. --- # # Detailed Content ## Pages > The page is not exist, and you got lost. Still, you can help your emails to find the primary inbox of your recipients with Warmy.io. - Published: 2025-03-20 - Modified: 2025-04-10 - URL: https://www.warmy.io/blog/404-you-got-lost/ 404 Lost in space? The page you requested could not be found. Back to home --- > Explore Warmy.io's blog for expert tips on boosting email deliverability with our AI-powered warm-up tool and best practices for inbox success. - Published: 2025-03-07 - Modified: 2025-07-11 - URL: https://www.warmy.io/blog/ Warmy Blog AllEmail DeliverabilityIndustry insightsInside WarmyMarketingOtherAllEmail DeliverabilityIndustry insightsInside WarmyMarketingOtherV Stay up to date Subscribe to Warmy. io's newsletter for weekly insights on mastering email deliverability *You can unsubscribe anytime --- --- --- ## Posts > The Warmy Research Team conducted an experiment to uncover which among different SMTP providers result in a faster delivery to Yahoo inboxes. - Published: 2025-07-07 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/the-fastest-path-to-yahoo-inboxes/ - Categories: Blog - Tags: Industry insights The Warmy Research Team conducted an experiment to uncover which among different SMTP providers result in a faster delivery to Yahoo inboxes. With around 230 million active users and a significant share of the email market, Yahoo Mail is definitely still a major player in the email service provider (ESP) market. Whether it’s for marketing campaigns, lead generation efforts, or customer updates, getting your emails to land in Yahoo inboxes is of the essence. Delays and detours to the spam folder can impact your open rates, click-through rates, and ultimately, your business bottom line. The Warmy Research Team, in constant pursuit of deliverability solutions, conducted a thorough analysis and experiment to uncover which among different SMTP providers result in a faster delivery to Yahoo inboxes. We compared several critical factors, such as IP type, sending balance, and template settings, to determine which configurations result in the fastest inbox placement. The key players of the experimentGetting emails to land in Yahoo inboxes is crucial—less ideal situations like delays or emails landing in spam result in missed opportunities and less ROI. This research aimed to dive into the key factors influencing how quickly emails reach the Yahoo inbox. The goal? To identify the best combination of provider and other particular settings that will result in the fastest inbox delivery. Our research focused on three widely used SMTP providers: SendGridMailGunCustom SMTP As for the other factors, we analyzed these variables:IP pool type (Dedicated vs. shared)Warmup template type (Custom vs. default)Sending balance (Balanced vs. unbalanced)IMAP status (Enabled vs. disabled)The IP pool showdown: dedicated vs. sharedWhen it comes to Yahoo inbox placement, the choice between a dedicated... --- > This email deliverability roadmap is designed to help senders optimize each stage of the email marketing journey. - Published: 2025-07-01 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/email-deliverability-roadmap/ - Categories: Blog - Tags: Email Deliverability We’re sure you know what we mean when we say ‘sending a message is just half the battle’ especially if you are into email marketing or email outreach. The true struggle is making sure that message not only makes it into the recipient’s inbox but that it gets opened, read, and that it stirs the necessary action. If your emails are not getting delivered into the inbox, the odds of generating leads, driving engagement and converting prospects simply go down. Deliverability impacts the complete email journey and the bottom line of your business. So we created this roadmap designed to help senders optimize each stage of your email marketing journey. You'll learn how to:Consistently land your emails in inboxesBoost your opens and clicks. Drive more conversions from cold emailsKey deliverability statistics to look atFor you to have an accurate idea of how effective your email marketing have been, it is essential you monitor crucial metrics across your email’s path. These are the numbers that provide insights about your email performance and where there is room for improvement. Open rateThis pertains to the percentage of recipients who opened your email. Consistently high open rates mean your emails are making it into the inbox successfully and that your subject lines make people want to read the rest of your message. Low open rates could mean your emails are not reaching the inbox, probably being rereouted to the spam folder, or that you should sharpen your subject lines. Click-through rate (CTR)This is the... --- > Warmy tested the impact of tracking links and tracking pixels on deliverability, as well as the impact of the "Show Image" prompt in tracking. - Published: 2025-07-01 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/impact-of-tracking-links-deliverability/ - Categories: Blog - Tags: Industry insights In cold email outreach campaigns, deliverability is a legit concern. And even after you draft the perfect email, the success of your campaign hinges on the email getting into the recipient’s inbox. But even if an email does make it to the inbox, there’s another challenge: tracking accuracy. For Gmail and Google Workspace (GW) users, a common issue arises from the "Show images" prompt. Open rates and click-through rates can't be tracked accurately until the prompt is clicked by the recipient. This is a problem for the marketers and salespeople who are attempting to quantify how successful their cold outreach campaigns are. In short, the prompt affects the actual open rates and click-through rates as they can seem significantly lower than they are—messing up your campaign performance data. The experiment: The impact of tracking pixel and tracking linkThe Warmy Research Team set out to determine the influence of tracking pixels and tracking links on deliverability, as well as if the “Show image” prompt influenced tracking and deliverability. To do this, the team sent out two templates each for each type of domain. Old domain/already warmed up:One without any links and was used to test sending only with the TP. One had links and was used to test both TP and TLNew domain/not yet warmed up:One without any links and was used to test sending only with the TP. One had links and was used to test both TP and TLThe importance of accurate tracking for cold outreachThe ability of senders... --- > When it comes to scaling email outreach, you need to calculate your ideal mailbox setup to avoid throttling and higher bounce rates. - Published: 2025-07-01 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/scaling-outreach-ideal-mailbox-setup/ - Categories: Blog - Tags: Marketing When it comes to scaling email outreach, you need to calculate your ideal mailbox setup to avoid throttling and higher bounce rates. The larger your outbound and outreach efforts become, the harder it is to manage your mailbox set-up. What starts as a simple system with one email address soon becomes more complex as you scale—or at the very least, as you start to add people to your team or take your brand into new markets. When it comes to scaling email outreach, it’s not just about scaling send volume—you need a strategy to prevent things like throttling, higher bounce rates, and getting flagged as spam. When you send more emails, you run into problems such as your email service provider’s email sending limits per day and the need to have more diverse, reliable mailboxes to handle the load. Domain reputation and how you use multiple mailboxes are defining factors that can make or break whether your messages are placed in the inbox or if they are thrown out completely. We’re going to guide you through scaling your mailbox setup properly. No matter if you're a startup with an aggressive sales plan or the sales team of a big company opening new territories, this guide will help to make your outbound explode sidewise at minimal risk and with maximum deliverability. Understanding the basics of scaling mailbox setupKnowing how to scale your email infrastructure correctly can be the difference between enjoying a well-earned spot in the inbox and falling victim to classic spam filters. With ⅔ of businesses sharing that email deliverability issues plague their revenue, understanding how to scale properly is even... --- > Learn how to do a basic email deliverability test, and explore the metrics you need to track and monitor for cold outreach success. - Published: 2025-07-01 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/beginners-email-deliverability-test/ - Categories: Blog - Tags: Email Deliverability Learn how to do a basic email deliverability test, and explore the metrics you need to track and monitor for cold outreach success. You spend a lot of time perfecting your email content. You're sure your recipients will want to book a call with you after reading your email. So you excitedly hit 'Send. ' A couple of days come and go and you are flustered at the absence of any scheduled meetings or calls—and you don’t understand what happened. Does this sound familiar? Perhaps you’ve been in such a position. Maybe you find yourself there nowWell, you're in the right place. There's a big chance your problems have something to do with your email deliverability. But before making any move, you ought to be certain. We’ll show you how to do a basic email deliverability test, and share with you some of the metrics that can determine email deliverability and how this affects your email outreach. When you’re finished, you’ll have the tools you need to begin testing your email like a professional. What is email deliverability testing? An email deliverability test lets you know just how well your emails land in inboxes. A deliverability test will examine your email's content, structure, authentication protocols (like SPF, DKIM, and DMARC), along with a bunch of other important things that affect placement inside the inbox. By running deliverability tests, you can:Identify deliverability issues before they hurt your campaigns. Monitor your inbox placement and detect if your emails are going to spam or are being blockedEnhance sender reputation by verifying correct authentication and adjust email content/frequency. Increase email engagement by getting your emails delivered and... --- > In this blog, we’re going to walk you through how to create an advanced email warmup strategy, designed specifically for cold outreach campaigns. - Published: 2025-07-01 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/email-warmup-strategy-and-tools/ - Categories: Blog - Tags: Marketing Email warmup is possibly the real unsung hero of cold email outreach. It is very easy for sales and marketing teams to become so engaged in generating the most perfect email content possible, creating the perfect segment, and running A/B tests like there's no tomorrow. But all of these efforts will be for naught without a strong warmup—those "perfect" emails will still land in spam. And if those emails go unseen, then they’re not going to deliver the results you're aiming for. In this blog, we’re going to walk you through how to create an advanced email warmup strategy, designed specifically for cold outreach campaigns. We'll also offer best practices for gradually increasing your email volume and explore some of the top email warmup tools that can automate this process, saving you time and effort while maximizing deliverability. What is email warmup and why is it important for cold outreach? Email warmup is the process of slowly ramping up send volume from a new or inactive domain to establish a positive reputation with Email Service Providers (ESPs). For cold outreach to work, your emails must be sent to inboxes where they stand the best chance of getting read and interacted with. If your emails are going to the spam folder, they aren’t going to be read, and you aren’t going to be getting any responses no matter how beautifully they’re written. A good warm-up plan enables you to slowly introduce your emails to ESPs so that your domain gains trust... --- > Learn how cold email sequencers contribute to your ROI and how you can execute them with Warmy's tools. - Published: 2025-06-30 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/how-cold-email-sequencers-boost-roi/ - Categories: Blog - Tags: Marketing Cold emailing delivers, so it's no surprise that it’s a common element in most outbound marketing strategies. Especially because you can reach hundreds (or even thousands) of prospects with just the push of a button. Whether you’re a sales group, a growth marketer, or a business owner, cold emails enable you to access a huge pool of prospects and get your product or service in front of a targeted audience. Now, throw automation into the mix, and the entirety of your cold outreach can look in a completely different. Taking your cold emailing outreach to autopilot with email sequencers will not only free your time, but also significantly increase your ROI. Featuring an ROI of $36 per $1 spent by email, your business is bound to excel. Automating makes it easy for sales to be able send personalized and timely follow-ups at scale and then track the success of every email campaign. What are cold email sequencers? Cold email sequencers are software for automating follow-up email messages to leads in a sequence of steps. They automate cold email outreach, giving you the infrastructure to engage with prospects over time, and maintain a level of organization and consistency. The ultimate objective is to encourage leads and move them through your funnel, without having to manually craft and send each email. For sales teams and lead generation professionals, sequencers automate a large chunk of repetitive and time-consuming tasks. With these tools, they can expand and refine their efforts to concentrate solely on... --- > Not all tools are created equal. Learn about the best email deliverability tools you can utilize to maximize your cold emailing and outreach efforts. - Published: 2025-06-30 - Modified: 2025-07-01 - URL: https://www.warmy.io/blog/best-deliverability-tools-cold-emails/ - Categories: Blog - Tags: Email Deliverability One of the most important things determining whether your cold email campaign will be successful or not is the deliverability. If your emails are not landing in your recipients’ inboxes, they’re not going to be opened and they’re not going to be read. Worse, they may wind up in spam or blacklisted—all your outreach efforts will be for naught. Email deliverability is more than a technical consideration. It is the prerequisite of ensuring your cold outreach is reaching the right people—in the first place. In the competitive landscape, getting to the inbox is as important as crafting the right message. Why email deliverability tools are necessary to reach the inbox There are so many moving parts between the moment you hit send and when your email lands in somebody’s inbox. Even more so if it is a cold outreach. If you don't have the proper tools, it can be almost impossible to guarantee that your emails are being opened, not getting caught by spam filters, and not building a bad reputation. Email deliverability software allows you to keep track of and test important aspects of your email campaigns such as domain reputation, spam score testing, inbox placement, and much more. Getting the right tools for deliverability won’t suddenly land you in inboxes out of thin air, but they can give you an edge. Key features of email deliverability tools Not all tools are created the same , but having a sense of the most prevalent factors impacting your deliverability can... --- > Email deliverability is essential for email marketing but it's a complicated concept for non-technical users. Here, we explain it in simple terms. - Published: 2025-06-30 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/email-deliverability-for-non-techies/ - Categories: Blog - Tags: Email Deliverability Email deliverability is essential for effective email marketing but it is also a complicated concept for non-technical users. Email deliverability is ensuring your cold outreach, newsletters, and promotional email actually make it into the inboxes of the right folks to see them. Even if your emails are the greatest piece of writing, you’re not going to get the engagement and the results that you want. This article breaks down email deliverability know-how to specifically help non-techies understand what exactly email deliverability is. By the time you’re done with this guide, you should have a simple, jargon-free plan to improve your email deliverability and spark your engagement rates. No coding or email systems experience required. What is email deliverability? First things first. There's a difference between email delivery and email deliverability. Email delivery rate simply pertains to the percentage of sent emails that were received by servers—without taking into consideration which folder they landed in. As long as the server received an email, that counts towards email delivery. On the other hand, email deliverability is the foundation of all successful email marketing initiatives. It is the process of ensuring your emails reach their intended destination: the recipient’s inbox. No matter how amazing your email’s content may be, it won't make any difference if your emails don’t make it to the inbox. Or worse, be completely blocked by email service providers (ESPs)—never reaching your audience. What can go wrong when your emails don’t make it to the inbox? Get caught in your... --- > Cold email is an integral part of any sales and marketing strategy. Learn how to execute cold email sequences that bring in results. - Published: 2025-06-25 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/cold-email-sequences-what-they-are-and-how-to-create-one-that-converts/ - Categories: Blog - Tags: Marketing Cold email is very much an integral part of any sales and marketing strategy this 2025. Despite the growing influence of social media and other digital channels, email still sits on the throne as the best way for businesses to reach out to prospects. In fact, email marketing has one of the best ROIs at a whopping $36 for every $1 spent, so it’s one of the most inexpensive ways to reach new leads and increase conversions. Then there’s cold email sequences—an entirely different world inside the bigger world of email marketing—that take the concept of cold email outreach to the next level. Understanding cold email sequencesA cold email sequence is a progression of strategically spaced emails that introduces you to leads followed by succeeding messages. Sequences can be applied in outbound sales, lead generation campaigns, and outreach for brand awareness. Rather than a single email, these sequences initiate a dialogue with the prospect and lead to better response rates and engagement. Cold email sequences are typically made up of three to seven emails sent over days or weeks. Every email is more valuable than the last, showing more of the product, focusing on a different angle and encouraging them to the next step of taking further action. But creating an effective cold email sequence isn’t easy. It's not only a matter of writing great copy. They involve timing, personalization, and follow-up tactics, and an understanding of the psychology behind why people respond to email outreach at all. The advantages of sequences over single emailsDid... --- > We’re going to seriously unpack cold email sequencers—what they are and why they’re insanely important when it comes to your outreach. - Published: 2025-06-25 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/cold-email-sequencers-for-outreach/ - Categories: Blog - Tags: Marketing Cold outreach is an essential technique for sales and marketing professionals who wish to create leads and build relationships at scale. But manual outreach—not to mention follow-up email management—can quickly spiral out of control. It’s labor intensive, prone to error, and can easily miss things. Cue cold email sequencers: the revolutionary tool that is changing how companies are—or should be—doing outreach. We’re going to seriously unpack cold email sequencers—what they are and why they’re insanely important when it comes to your outreach. Want to scale your outreach up with a bit more of a personal touch? Here’s more on how cold email sequencers can transform your cold outreach. Cold email sequencers: What are they? Cold email sequencers are powerful tools that automate the sending of a series of emails over a period of time. This way, outreach is done for you without you having to do any manual work. These are tools that enable you to create a series of emails for a certain purpose and send them on your schedule. Alleviating the need to manually follow up, cold email sequencers help facilitate outreach efforts, making them more efficient and effective. (Read more: The Perfect Cold Email Schedule Timing, Frequency & Follow-Ups)The basics of cold email sequencingCold email sequencing is the process of writing out a number of emails to be sent to prospects in a specific order, over a period of time. The sequence will usually start with an intro email and follow-up emails aim to generate more and more interest. Cold email... --- > A mailbox calculator helps email marketers optimize their sending volume while protecting their sender reputation. Learn more here. - Published: 2025-06-24 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/mailbox-calculator-explained-what-it-is-and-why-email-marketers-use-it/ - Categories: Blog - Tags: Marketing For email marketers, here’s a common dilemma: Finding the balance between sending just the right amount of emails to engage prospects while staying within the limits to ensure deliverability. It can be challenging, and that’s where a mailbox calculator comes in. A mailbox calculator is a tool designed to help email marketers optimize their sending volume while protecting their sender reputation. With two out of three businesses sharing that email deliverability issues hurt their reputation, it only makes sense to cover all bases—mailbox management included. Understanding how many mailboxes you should use for cold email outreachIn any cold email outreach, finding the optimal amount of mailboxes to use (not too many, but not too few either) is a must to keep your deliverability high and campaigns effective. Proper management of the number of mailboxes also allows you to avoid triggering spam filters and keep your domain or IP in a favorable light. The risks of using too many mailboxesIt might be tempting to use more mailboxes to spread the load out and crank up the email sends, but using too many can come with its own negative consequences:Overhead and management complexity: Each additional mailbox requires more oversight, time, and resources. You can potentially find yourself in the middle of uneven email distribution or neglecting some mailboxes altogether, which can lead to inconsistencies in deliverability. Mailbox rotation problems: If you fail to rotate mailboxes correctly, some mailboxes may be underused, while others may be overused. This can send alarms to email service... --- > For startups and solo founders who wear multiple hats, email deliverability issues must be a priority before they cause long-term damage. - Published: 2025-06-21 - Modified: 2025-06-23 - URL: https://www.warmy.io/blog/email-deliverability-demystified-a-simple-guide-for-startups-solo-founders/ - Categories: Blog - Tags: Email Deliverability Whether sending cold emails to generate leads, newsletters to engage your audience, or outreach to potential investors—email deliverability is critical to making sure you get noticed and actually get the engagement you need. After all, email has an ROI of $36 per $1 spent so it’s no wonder solo founders and startup CEOs want in on that action. But if your emails are consistently ending up in the spam folder or promotions folder, and never landing in the intended recipients’ inbox, it will all be in vain. And the fact is, email deliverability is one of those under-the-hood parts of your outreach strategy that can mean the difference between the success or failure of your efforts. For startups and solo founders who wear multiple hats, email deliverability issues can fly under the radar until it’s too late. What is email deliverability and why does it matter? Email deliverability refers to whether or not the emails you send end up in your recipient’s inbox, or if it is blocked, or sent to spam (or any other prebuilt folder such as promotions). Read more: Email Deliverability: Complete Guide for 2025 It’s a vital measurement for any email marketing or outbound outreach campaign. If your emails aren’t landing in a recipient’s inbox, they can’t do the job you need them to do. In other words: High deliverability = more opportunities of emails making it to the inboxes  Low deliverability = more of your emails are likely to hit the spam folders The way forward is clear—high... --- > Learn how many mailboxes you should use for your cold email outreach strategy to succeed. Plus, see how a Mailbox Calculator can help. - Published: 2025-06-20 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/how-many-mailboxes-do-you-really-need-for-email-outreach/ - Categories: Blog - Tags: Marketing With all the focus on content, subject lines, and targeting, it seems that we usually overlook the role that your email infrastructure—your mailboxes, that is, your recipients—plays in the success of your email campaigns today more than ever. All of these factors make it crucial to have accurate mailbox planning, which will ensure your emails land in inboxes and avoid being flagged as spam. One wrong step and your open rates could drop through the floor, your bounce rates could soar, and you could find your sender reputation in tatters. One mistake commonly made by businesses is to overload one mailbox by sending too many emails from it. This can backfire and set off the spam filters and send your emails to the spam folder. On the other end, having too many mailboxes can create clutter—making outreach management a challenge and adding bloat to the workflow. In this guide, we’ll help you figure out how many mailboxes you should actually use for your outreach strategy to succeed. We’ll also show you some mailbox warm-up tools that can help you guarantee that your emails are being sent from trustworthy, well-maintained mailboxes. Let’s take a deep dive into your mailbox management needsWhen it comes to devising a strategy for your email outreach, it’s worth keeping in mind that mailbox management is not a one-size-fits-all type of strategy. The number of mailboxes you need depends on the size of your team, your outreach goals, and the volume of emails you plan to send. Mismanagement and oversight... --- > Don’t let a flawed cold email template ruin your outreach. Use Warmy.io’s built-in deliverability tools before launching your next campaign. - Published: 2025-06-18 - Modified: 2025-06-30 - URL: https://www.warmy.io/blog/is-your-cold-email-template-getting-you-marked-as-spam/ - Categories: Blog - Tags: Email Deliverability When it comes to cold outreach, many marketers and sales teams focus on the quality of the email list. But, here’s some real talk. No matter how great your connections are, your cold email template can make or break your dreams. You may be sitting on a goldmine of perfect prospects, but if your email template isn’t set up for deliverability, your message may never even end up in their inbox. Given that approximately 45. 6% of emails worldwide were classified as spam, who’s to say your emails are guaranteed to land in your target inboxes? Spam filters have become more intelligent and even more sophisticated. They can now identify the usual patterns that spammers have been using over time. So even if your email isn’t really spam, or even if you’re the most legitimate sender ever, certain elements can make your email look like unsolicited marketing. The top spam triggers in cold email templatesIf you’re dabbling in cold outreach, you need to know how to avoid common spam triggers. We’re talking about certain words, formatting tactics, and specific elements that can cause ESPs to flag your email as spam. Related Reading: Words That Trigger Spam Filters (And How to Fix Them with a Template Checker)Here are some of the most common spam triggers to watch out for:Spammy words and phrasesSpam filters scan emails for certain phrases and language that are usually used in marketing or advertising emails. Common spammy words include:FreeGuaranteeLimited time offer100% satisfiedClick hereEarn moneyNo costAct nowSo what happens... --- > Learn why mailbox calculators are important for cold email strategies, how they work, and how to use them along with other warmup tools. - Published: 2025-06-18 - Modified: 2025-06-18 - URL: https://www.warmy.io/blog/why-your-cold-email-strategy-needs-a-mailbox-calculator-and-how-to-use-one/ - Categories: Blog - Tags: Marketing Cold email outreach is not just about writing the perfect message—it’s about the “machine” behind that message. The most common error in outbound email outreach is miscalculating how many mailboxes you require. This in turn can lead to spam flags, bounce rates, and, eventually diminished campaign performance. To be able to scale cold email outreach and keep your sender reputation high, you have to structure your email infrastructure properly. That’s where the mailbox calculator comes in—the underrated device that ensures your outreach is both scalable and safe. In this guide, we will go into why mailbox calculators are important for cold email strategies, how they work, and how to use them along with other mailbox warm-up tools to avoid potential mistakes. The importance of infrastructure in cold email outreachWhen you’re planning a cold email campaign, a lot of times you’ll find yourself focusing on nailing the subject line or the perfect call-to-action (CTA). Related Reading: 14 Tips For Writing An Excellent Email Subject Line + ExamplesBut what’s just as vital—if not more so—is laying a strong foundation for your email campaigns. Even the most carefully created emails can wind up in the spam folder, or, worse, get blacklisted without the right infrastructure. Then you’re potentially in for a world of hurt. Two out of every three businesses say that email deliverability problems damage their revenue. So what’s the solution? Here’s the real deal—email deliverability is like an onion. There are just too many variables that make it work or fail. It could... --- > Learn all about email deliverability basics that will help you avoid spam folder and improve email deliverability. - Published: 2025-06-16 - Modified: 2025-06-16 - URL: https://www.warmy.io/blog/from-spam-folder-to-inbox-mastering-email-deliverability-basics/ - Categories: Blog - Tags: Email Deliverability It can be really frustrating when you realize your emails are being reported as spam. Because no matter how hard you’ve worked, it all goes to waste if your emails don’t reach the inboxes. Mastering email deliverability is now essential, and no longer optional—an ROI of $36 ROI per $1 spent is very valuable for businesses. With poor deliverability, you will not get a share of that revenue pie. The thing is, email deliverability isn’t just about creating emails and hitting ‘Send. ’ It’s about ensuring they actually get opened. It’s achieving that balance of technical factors, best practices, and continuous monitoring. Ready to start landing in inboxes? Let’s dive in! Why email deliverability mattersWe’ll try to keep this simple:High deliverability: higher likelihood of emails landing in the inbox. Low deliverability: more chances of your emails landing in spam The real impact of low deliverabilityLower open rates: If your emails are landing in the spam folder or being blocked by email providers, they’re not getting opened. The average open rate is 19. 21%—if you see your open rates consistently decreasing, there’s something wrong. Fewer conversions: It follows. When emails don't reach the inbox and they don’t get opened, then there will be no chances to convert leads. Missed opportunities: Each email that doesn't make it to the inbox is a missed opportunity. Damaged reputation: A consistent track record of low deliverability can damage your sender reputation with email service providers (ESPs). Over time, poor deliverability can result in your emails... --- > Email signature deliverability contributes to the success of your email outreach. Learn how you can craft signatures that avoid spam filters. - Published: 2025-06-16 - Modified: 2025-06-17 - URL: https://www.warmy.io/blog/build-a-signature-that-works-for-email-outreach/ - Categories: Blog - Tags: Email Deliverability Your email signature can feel like an afterthought when it comes to cold outreach emails. It’s just an easy sign-off at the end of your message, right? Wrong! It’s much more than that, actually. Your email signature is one of the fundamental factors that helps determine your deliverability—whether your email ends up in the recipient’s inbox or spam folder. The truth is, if you have a solid email signature, your deliverability can go through the roof, your credibility goes up, and you might even get a few more responses. In the cold outreach universe, every little thing counts. Having your name and contact information are not enough. You also need to make sure that your signature aligns with the standards of Email Service Providers (ESPs) that determine whether you end up in a user’s inbox or not. The anatomy of an outreach email signature that worksA well-designed email signature is simple, professional, and believable. The correct elements will not only boost the credibility of your email, but will also help your email dodge the spam filters of your target inboxes. Essential elements:Contact email: This is an email address through which your recipient can contact you. Having this in your signature reassures email service providers (ESPs) that you are a legitimate sender, not a spammer. Phone number: Providing a contact number (business or mobile) adds some legitimacy to your email. It provides recipients with another means of confirming your legitimacy and reaching out. Company name: Providing your company name in the signature tells the recipient that you are a... --- > Warmy tested six different email signature templates across various providers to discover how signatures affect deliverability across ESPs. - Published: 2025-06-13 - Modified: 2025-06-16 - URL: https://www.warmy.io/blog/signature-showdown-crafting-the-perfect-email-signature/ - Categories: Blog - Tags: Industry insights In a world where email marketers compete for open rates, click-through rates, and conversions, the email signature may easily be overlooked. Or it may even be a last-minute addition. However, did you know it could actually be the difference between your email landing in the inbox or getting lost in the spam folder? The battle for the inbox Does your signature help you establish trust? Does it make your email look legitimate? Or, does it raise red flags that send your message straight to the spam folder? Also, what is it about certain email signatures that can tip the scales in your favor? What makes one signature type more effective than another? These are the questions that the Warmy Research Team seeks to answer in the latest report. The showdown: How signatures affect deliverability across ESPs This experiment tested six signatures and one baseline across OpenSRS, Microsoft365, and G Suite. All templates were in plain text format and each signature contained the name of the recipient and the sender. The baseline template had no signature. Here is a quick look at what each email signature template looks like: Ready to see how your email signature stacks up in the battle for the inbox? Let’s dive in! The key players: What goes into an email signature? In the showdown of email signatures, every element of your signature plays a vital role. Let's break down the essential components of an email signature and explore their impact on inbox placement. Contact information: The... --- > Cold outreach through email marketing is still a cornerstone of sales and marketing in 2025. With an ROI of $36 per $1 spent - Published: 2025-06-11 - Modified: 2025-06-11 - URL: https://www.warmy.io/blog/cold-email-campaigns-vs-cold-email-sequences-whats-the-difference/ - Categories: Blog - Tags: Email Deliverability Cold outreach through email marketing is still a cornerstone of sales and marketing in 2025. With an ROI of $36 per $1 spent, it's an excellent strategy for engaging new leads, growing brand awareness, and driving conversions. But we see a lot of confusion between “cold email campaigns” and “cold email sequences. ”People tend to confuse them, but the jobs that they do are different. Now, labels are just that—labels for the sake of argument—but the distinction is useful for clarifying your strategy. We'll break down the differences between the two—campaigns, which are one-off or bulk sends, and sequences, which are a series of follow-ups. We’ll also share when to use each, their pros and cons, and how combining both can supercharge your outreach. If you’re already familiar with cold email but want to revamp your approach, this article can help you decide on the best approach for your needs. And if you’re still trying to decide whether to dip your toes in cold outreach or not, this guide will show you what’s possible. What is a cold email campaign? A cold email campaign is a one-time or bulk email sent to a list of cold leads— typically in the hopes of introducing your product, service, or announcement to a new audience. Cold email campaigns are frequently used for promotions, generating leads or sharing. Key characteristics of a cold email campaignOne-off nature: Cold email outreach is usually just that—a one-off mass message sent to a batch of leads or a specific segment of them. Same message... --- > Explore how signature builder tools can help improve your deliverability and overall success of your cold email outreach. - Published: 2025-06-11 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/signature-builder-tools-what-they-are-how-to-use-them/ - Categories: Blog - Tags: Email Deliverability, Other First impressions count in cold outreach. From your subject line to your sign-off, everything in the email you send to a potential lead is being put under the microscope. Sales reps spend around 21% of their day writing emails, which is a reflection of how much people value good copywriting. But there’s an often-forgotten element that can have a major impact: your email signature. A high-quality, designed email signature gives cold email credibility to your message and helps you look trustworthy and dependable to busy people. But the fact is, you may not have a lot of experience in designing an email signature—and it isn’t always easy to create a professional-looking one. That’s where email signature builder tools come in. They make it easy to create an attractive, professional email signature that not only looks good but also reflects your brand and makes you stand out. What are signature builder tools? An email signature generator is a tool or an application that helps you create a professional and customized email signature in minutes—even if you’re not a designer or don’t have coding or technical skills. These tools allow you to design email signatures more quickly by offering predesigned templates with easy-to-navigate customization and formatting. No matter if you’re a solopreneur, a sales person or marketer, these tools ensure you always develop an impactful email signature. These tools typically feature a simple drag and drop interface to personalize your signature based on your name and title, company details, and anything else useful like phone... --- > Timing is everything when it comes to cold email outreach. An email can be perfectly composed but it won’t be effective - Published: 2025-06-10 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/the-perfect-cold-email-schedule-timing-frequency-follow-ups/ - Categories: Blog - Tags: Marketing Timing is everything when it comes to cold email outreach. An email can be perfectly composed but it won’t be effective if it's sent at the wrong time. Meanwhile, the right schedule can greatly increase your open and response rate. But, when should you send those emails, when should you follow up and when do you throw in the towel? The solution is to streamline your outreach schedule and do your best to walk that fine line between being persistent and respecting your prospect’s time. This blog will guide you through the science of cold email timing and offer insights into how to structure your follow-ups for maximum engagement. Whether you are an experienced sales rep or a beginner, learning the art of scheduling cold emails is a must if you want to achieve success in your outreach. The science behind cold email timingWhen it comes to cold-email outreach, timing is more than just a matter of convenience. It’s a critical factor, capable of making or breaking the success of your campaign. Becoming familiar with when to send your cold emails, how often to follow up, and when to give prospects a little bit of breathing room involves some heavy data number crunching and an understanding of human behavior. How timing affects open and response ratesIt’s not just about timing when you send an email. Timing affects whether or not the recipient opens it, clicks the links, or even responds. The open rate is the first metric to be impacted by timing, but click-through rates... --- > Email deliverability can be the difference between success or failure of your outreach. You could be doing everything perfectly. - Published: 2025-06-10 - Modified: 2025-06-19 - URL: https://www.warmy.io/blog/why-your-email-signature-might-be-hurting-your-deliverability/ - Categories: Blog - Tags: Email Deliverability Email deliverability can be the difference between success or failure of your outreach. You could be doing everything perfectly. Amazing copy, highly targeted prospects, awesome sending infrastructure—and still, your emails land in spam. Why? One source you may not have considered: your email signature. That little block of text (and sometimes images) at the bottom of your message may appear harmless. But to email providers, it’s a potential red flag—especially in cold outreach campaigns. In this post, we’ll cover how your email signature might be harming your deliverability behind the scenes, mistakes to steer clear of, and how you can create a crisp, compliant, and deliverability-friendly signature that also looks professional. Let’s dive in. Email signature mistakes that harm deliverabilityEven a well-intentioned email signature can become a liability if not designed with deliverability in mind. Signatures should look professional and informative, but design and content decisions can trigger spam filters or erode trust with email service providers. Here are the most frequent signature blunders we see:Overuse of linksEach link in your email increases the scrutiny from spam filters. When your signature has more than one link (your website, LinkedIn, your Instagram, and so on), it sounds the alarm. Why? Because links in an email are a signature of spam, phishing and mass marketing efforts. One to two relevant links should be enough. Embedded or hosted imagesThere’s a good chance that having images (such as logos, badges, or banners) in your signature may look professional, but may also ruin your email’s deliverability.... --- > When it comes to cold email outreach, the devil is literally in the details. From the subject line to the body copy - Published: 2025-06-06 - Modified: 2025-06-06 - URL: https://www.warmy.io/blog/email-signature-best-practices-for-cold-outreach-campaigns/ - Categories: Blog - Tags: Email Deliverability When it comes to cold email outreach, the devil is literally in the details. From the subject line to the body copy, your message should immediately call attention and build trust. One detail often forgotten that actually has a huge role is the email signature. While it may seem like a small detail, a fantastic email signature can have a huge effect on the success of your outreach. Did you know that only 8. 5% of cold emails get replies? All the more reason to pull out all the stops in trying to get an answer. A good business email signature enhances your brand, gives people information about you and your business, and facilitates people taking action. It sends a powerful reputation signal that not only helps in establishing trust but also in being seen as a legitimate, reputable sender. After all, in the dog-eat-dog realm of cold emailing, the small touches can make a big difference. In this post, we will leave no stone unturned when it comes to creating an email signature that’s tailor-made to your cold outreach campaigns. We’ll cover the key details to include, offer a little inspiration, and give you some actionable tips to make sure your email signature is working for you. Key elements of a high-performing email signature for cold outreachYour email signature is usually the last thing someone sees, yet it demonstraes the professionalism and the kind of brand you’re representing. In this section, we will dissect the key components that form a high-performing email signature for... --- > The success of your email marketing efforts depends a great deal on your email deliverability. No matter how strong your message is - Published: 2025-06-06 - Modified: 2025-06-06 - URL: https://www.warmy.io/blog/email-deliverability-testing-101-tools-metrics-what-you-should-be-looking-for/ - Categories: Blog - Tags: Email Deliverability The success of your email marketing efforts depends a great deal on your email deliverability. No matter how strong your message is, if it’s not getting into the inbox, you’re wasting your time. In 2025, the world has around 4. 6 billion email users. Now, when 45. 6% of global emails end up in spam, you see why email deliverability is no easy feat. We’ll explain what email deliverability testing is, why it matters, and the most important performance benchmarks you should be monitoring to see if your emails are doing all they can for you. We’ll also show you the best tools and resources at your disposal to run tests and increase your email deliverability. And by the end of this guide, you’ll be an expert at how to read your test results and what you can do to take action to remedy any problems so your emails end up where they’re supposed to, not lost in the internet's black hole. What is email deliverability and why does it matter? Email deliverability: Emails are actually reaching your recipients’ inboxes rather than bouncing or being sent to the spam folder or junk folder. This isn’t even a question of whether or not your emails were sent. It’s whether or not they’ve been received by the email server, and made it through the spam filters that decide whether your messages are allowed in. If your emails are consistently blocked or filtered as spam, it can damage your sender reputation and hurt your long-term email engagement.... --- > When it comes to cold email outreach, the name of the game is deliverability. It doesn't matter how compelling your message - Published: 2025-06-04 - Modified: 2025-06-04 - URL: https://www.warmy.io/blog/write-better-cold-emails-using-a-template-checker-to-boost-deliverability/ - Categories: Blog - Tags: Email Deliverability When it comes to cold email outreach, the name of the game is deliverability. It doesn't matter how compelling your message is or how great of a cold email you send if it doesn’t get to your prospect's inbox. In fact, even seemingly minor problems in your email template can lead to the biggest deliverability headaches and your painstakingly planned campaigns could end up in the dreaded spam folder of your target audience instead. That’s why a cold email template checker comes in handy. It scans your emails and followups before you send them—detecting spam triggers, forgotten personalization opportunities, and formatting problems that can dampen your engagement. Tired of spending time on cold email campaigns that just never get read or don't get a response? Let’s go even deeper on how template checkers can change the game in your cold email strategy. What is a cold email template checker? A cold email template checker is a program specifically created to assess the content, structure, and other components of a cold email before it’s sent. The goal is to maximize deliverability of the cold sales email template. The role of a cold email template checker is to help you identify and repair potential issues that might ruin your email marketing efforts. It scrutinizes for errors that are commonly made (using certain spammy words, incorrect email structure, or lacking personalization chances) and offers you options to do better. This means you can send emails that are much more likely to land in an inbox... --- > The truth is, most of the people that get into marketing are not big math lovers. Numbers, formulas, and equations can feel like a language - Published: 2025-06-04 - Modified: 2025-06-04 - URL: https://www.warmy.io/blog/mailbox-math-how-to-optimize-sending-volume-without-hurting-deliverability/ - Categories: Blog - Tags: Email Deliverability The truth is, that most of the people that get into marketing are not big math lovers. Numbers, formulas, and equations can feel like a language you would rather not learn when you would rather be writing compelling messages or building relationships. Naturally, marketers are much more keen on math when it exposes things like:The ROI for email marketing is $36 per $1 spent. There are approximately 4. 6 billion email users in the world in 202559% of consumers admit promotional emails are a big factor in their purchase decisionsWhat do these numbers mean? And the answer is simple—email marketing delivers business growth. That’s why when it comes to email marketing it really helps to understand a little bit of what we call “mailbox math. ”We’ll break down the math behind email sending volumes and show you practical strategies for pacing your campaigns to maximize deliverability. Plus, we’ll introduce how automation tools like Warmy’s mailbox calculator can take the guesswork out of the equation, helping you send smarter and safer—even if math isn’t your favorite subject. What is mailbox math? Mailbox math is the sum of the numbers and variables that marketers factor in to figure out exactly how much mail is “too much” without hurting their email sender reputation or deliverability. It’s the “science” of pacing your email sends and making sure you hit enough prospects—but not too many to trip spam filters. Q: What are spam filters? A: Spam filters are used by email service providers to detect and block unwanted or suspicious... --- > Learning how to implement cold email outreach is imperative for any person in marketing, sales, or any entrepreneur who wants to grow - Published: 2025-06-04 - Modified: 2025-06-04 - URL: https://www.warmy.io/blog/the-anatomy-of-a-high-performing-cold-email/ - Categories: Blog - Tags: Email Deliverability Learning how to implement cold email outreach is imperative for any person in marketing, sales, or any entrepreneur who wants to grow their business. After all, with an ROI of $36 per $1 spent, email marketing is simply a revenue bomb. But writing a cold email that grabs attention and gets a response isn’t as simple as sending a generic message to hundreds of leads. The old days of "spray and pray" are long forgotten. It’s simple: Cold outreach success is rooted in the ability to create an effective email—one that speaks to the reader and lands in their inbox, not the spam filter. in this guide, we’re going to break down the components of a successful cold email. From the subject line that snags attention, to the body copy that delivers value—every piece of your email has a job to do when it comes to engaging recipients. We’ll dissect each element and demonstrate how to optimize it for maximum impact. By the time you've finished reading this, you’ll understand how to structure your cold emails for success. Plus, we’re including a high-performing sales email template that you can customize for your own outreach efforts. Key elements of a high-performing cold emailTime to don our “email doctor” hats and get to it. It’s our job as email doctors to take a look under the hood of the anatomy of a cold email to make sure that all of the parts are healthy and operating at peak efficiency. Let's take a look at each... --- > Email deliverability—one of the most critical factors in the success of email marketing campaigns, yet often the hardest to maintain - Published: 2025-06-03 - Modified: 2025-06-03 - URL: https://www.warmy.io/blog/how-to-spot-deliverability-issues-before-they-tank-your-campaign/ - Categories: Blog - Tags: Email Deliverability Email deliverability—one of the most critical factors in the success of email marketing campaigns, yet often the hardest to maintain. Even the most minor blip in inbox placement can have a serious impact on your bottom line. You don't want to miss out on that magnificent email marketing ROI—$36 ROI for every $1 spent. There are ways of getting around deliverability problems, but the major issue here is seeing it coming before it becomes a disaster for your campaigns. Waiting until you see a dip in engagement or an uptick in bounce rates may be too late. By the time you respond, you could end up with a bad sender reputation, and it might take several weeks to get back into the good graces of email service providers. In this guide, we’ll show you how to spot red flags early on so you can take action before deliverability issues sabotage your email campaign performance. 4 common signs of email deliverability red flagsf you’re not keeping an eye on these critical metrics, you may overlook early warning signs that your emails aren’t doing much to reach your target audience. Here are some common red flags that signal you have potential deliverability challenges:Sign #1: Your open rates are droppingIf your open rates are slipping, you are likely stuck in an email marketing "rut. " When you have a sudden slump in your open rates or engagement, that’s a pretty good sign that your emails aren’t making it to where they’re supposed to go. If you see that receivers are... --- > An email signature is not just a line with contact info at the end of your cold email, is so much more. It’s part of the first-hand impression - Published: 2025-06-03 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/the-power-of-a-great-email-signature-in-building-trust-with-cold-leads/ - Categories: Blog - Tags: Marketing An email signature is not just a line with contact information at the end of your cold email, its so much more. It’s part of the first impression that you give. In essence, a professional email signature that’s well designed can help establish trust with leads that you haven’t connected with yet. Succeeding in cold outreach is all about trust. Without that, whatever you have to say may never even be read. Additionally, only 8. 5% of cold emails get replies. A good email signature not only adds credibility. It also makes communicating with prospects or even customers a more personalized experience. In this post, we'll look at why a great electronic signature is important, what to include in one, what not to do, and how automated tools, such as Warmy. io, can help you streamline your signature and send cold emails that look professional. Why a professional email signature mattersYour email signature isn’t just a sign-off, it’s a tool that levels up your email communication. It can influence how recipients think of you and your company. For cold leads in particular, a good signature can mean the difference between establishing trust and being ignored. Here are the top reasons that will help you understand the importance of taking the time to create a professional email signature:Establishes credibility at a glance: A crisp, professional looking signature says “I’m real, I’m legit and you can trust me” in a moment. And this is what makes cold leads feel more comfortable communicating with... --- > If your means of business communications includes emails, it is important to secure your domain from bad actors. - Published: 2025-06-03 - Modified: 2025-06-03 - URL: https://www.warmy.io/blog/set-up-dmarc-in-5-minutes-with-a-generator/ - Categories: Blog - Tags: Email Deliverability If your means of business communications includes emails, it is important to secure your domain from bad actors. DMARC (Domain-based Message Authentication, Reporting & Conformance) is a really helpful feature that you can use to avoid having your email spoofed by attackers and used for sending phishing emails. It also makes you more likely to land in your customers’ inboxes than spam folders. But DMARC can be a pain to set up. Particularly if you don't have a technical or web design background. Plenty of small business owners, marketers, and entrepreneurs are scared of the jargon, coding, and potential mistakes that could throw them off track. This guide changes that. We’ll demonstrate how you can get up and running with DMARC record in only five minutes with the help of a user-friendly DMARC generator tool. No coding skills required. By taking a few simple steps, your email domain will be secure, your brand will be safe from harm, and your emails will find safe passage to the recipient’s inbox—with no time lost to stress or misunderstandings. Ready to get started? Let’s demystify DMARC and make your email safer today. What is DMARC? A simple explanationIn Q4 of 2024, there were over 989,000 unique phishing attacks across the globe. This translates to major breaches—in fact, the average cost of a data breach against a company can go over $4 million. Spoofing occurs when attackers send emails that appear to come from your business. Phishing employs these forged emails to provoke your customers into divulging sensitive info. Implementing DMARC... --- > Every marketer wants to know their email campaign is well-received, lands straight in the inbox, and gets the recipients to take action. - Published: 2025-05-30 - Modified: 2025-05-30 - URL: https://www.warmy.io/blog/words-that-trigger-spam-filters-and-how-to-fix-them-with-a-template-checker/ - Categories: Blog - Tags: Marketing Every marketer wants to know their email campaign is well-received, lands straight in the inbox, and gets the recipients to take action. But even with all your best efforts, many of those emails still fall into the black hole of the email world—the dreaded spam folder. And they are never read by your audience. One common cause? Certain words and phrases that trigger spam filters. Spam filters are constantly crawling all over the words in your emails, searching for language that is usually a sign of a bad or deceptive message. Using too many “spam trigger words” can decrease your email’s likelihood of hitting the inbox, thus, reducing your open rates and overall campaign performance. The good news? You no longer have to wonder which words are endangering your emails or scour your content by hand. If you have the right tools, such as a template checker, you’re able to automatically detect risky language, receive safer alternative suggestions, and fine-tune your emails to fly under the radar of spam filters without losing the message's power. Understanding spam filters and trigger wordsSpam filters serve as the bouncers of your recipients’ inboxes. Their job is to keep out unwanted or dangerous emails, but they sometimes end up blocking even the good-old marketing emails that recipients signed up for. Q: What are spam filters? A: Spam filters are mechanisms used by email providers to identify and filter out undesirable or potentially harmful emails before they reach a user’s inbox. Related Reading: Spam filters: everything you need to... --- > Email is one of the most powerful tools for communication. However spam, phishing, and spoofing continue to be an ongoing risk - Published: 2025-05-30 - Modified: 2025-05-30 - URL: https://www.warmy.io/blog/how-to-use-an-spf-generator-to-protect-your-domain-and-improve-inboxing/ - Categories: Blog - Tags: Email Deliverability Email is one of the most powerful tools for communication. However spam, phishing, and spoofing continue to be an ongoing risk not only to your domain’s reputation, but also to your email deliverability. Of the more than 3. 4 billion emails sent daily with good enough forgery to make them look like they are from someone you trust, the threat of phishing should not be taken lightly. That’s where SPF (Sender Policy Framework) comes in—to the rescue. SPF is an important email authentication protocol that establishes which mail servers are allowed to send email on behalf of the domain. When properly set up, an SPF record is an effective tool in helping you protect your domain from being used for purposes you don't want (obscurity, phishing, etc) and increase the likelihood of getting in the recipient's inbox. The average cost of a corporate data breach is over $4 million—and this is a risk that companies are definitely not willing to take. Setting up SPF might sound complex or overwhelming, but it doesn’t have to be. With an SPF generator, it's a breeze. You can generate the exact SPF record easily no matter how little you know about SPF and without having to deal with guess work or syntax error. What is SPF (Sender Policy Framework)? Sender Policy Framework (SPF) is a critical email authentication protocol designed to help prevent email spoofing and phishing attacks. This is just one of the ways or criteria Google uses to block an estimate of 100 million phishing emails... --- > Email spoofing is possibly the biggest danger in email marketing. Not only does it put recipients at risk, it can also destroy a brand. - Published: 2025-05-30 - Modified: 2025-05-30 - URL: https://www.warmy.io/blog/dont-let-your-emails-get-spoofed-how-a-dmarc-generator-helps/ - Categories: Blog - Tags: Email Deliverability Email spoofing is possibly the biggest danger in email marketing. Not only does it put recipients at risk, it can also destroy a brand's image and email deliverability. Cybercriminals frequently pose as business or individuals in order to defraud receivers, capture sensitive data, or infect them with malware—in Q4 of 2024 alone, there were over 989,000 unique phishing attacks detected across the globe. Protecting your domain from spoofing is a critical move. It is no longer a choice—it is a requirement. DMARC (Domain-based Message Authentication, Reporting & Conformance) is a great solution to help combat email spoofing. By setting up DMARC, you can prevent any email spoofing attempt and ensure that only trusted email senders can send emails on your behalf, which strengthens your brand’s security and boosts email deliverability. What is email spoofing? Email spoofing is when a hacker or cyber criminal sends an email that appears to be from a trusted source. The goal of email spoofing? To deceive the recipient and get something. Spoofing, on the other hand, is when a fake “from” address is created in the email header. This then gives off the appearance that an email is real and from a legitimate source. The truth is, attackers don’t need access to your email account to accomplish this. They can impersonate any company or employees to use in their scams wherever they are. There are different types of scams that cybercriminals execute:Phishing: Emails that pretend to be from actual companies or businesses to trick people into giving personal... --- > If you’ve ever wondered why some domains warm up faster than others, you’re not alone. For marketers and businesses, speed to inbox - Published: 2025-05-30 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/cracking-the-inbox-code-what-speeds-up-outlook-delivery-from-different-smtp-providers/ - Categories: Blog - Tags: Industry insights If you’ve ever wondered why some domains warm up faster than others, you’re not alone. For marketers and businesses, speed to inbox can make or break a campaign’s success—especially when sending to major providers like Outlook. With more than 400 million active email users worldwide and an 8. 10% market share, getting your emails to land in Outlook inboxes are of the essence. Our Warmy Research Team conducted a detailed analysis comparing how fast emails get delivered to Outlook inboxes during the warmup process when sent through three popular SMTP providers: SendGrid, MailGun, and Custom SMTP setups. In this report-backed blog, we’ll reveal what affects inbox placement speed most significantly and which SMTP provider and settings combo yields the fastest results for Outlook. Ready to unlock the secrets to faster inbox delivery? Let’s dive in. The research rundown: Why speed to inbox mattersGetting your emails into the Outlook inbox quickly is critical for timely engagement, especially for marketing campaigns, transactional emails, and important notifications. Delays or landing in spam can mean missed opportunities, lower open rates, and diminished ROI. Related Reading: Improve Email Deliverability in OutlookThe key question: Which combination of provider and settings gets your emails delivered fastest? To identify the best approach, our research focused on three widely used SMTP providers: SendGridMailGunCustom SMTP We analyzed multiple variables, including:IP pool type (Dedicated vs. shared)Warm-up template type (Custom vs. default)Sending balance (Balanced vs. unbalanced)IMAP status (Enabled vs. disabled)IP pools unpacked: The inbox race between dedicated vs. sharedUnderstanding these types matters... --- > We’re certain you’ve experienced this scenario too many times before. You’re looking forward to checking the open rates - Published: 2025-05-28 - Modified: 2025-05-28 - URL: https://www.warmy.io/blog/how-a-template-checker-can-save-your-email-campaigns/ - Categories: Blog - Tags: Marketing We’re certain you’ve experienced this scenario too many times before. You’re looking forward to checking the open rates and clickthrough rates of your latest campaign, and instead you encounter a high spam folder placement rate. What went wrong? Often, it’s not your strategy—it’s your template. Email templates are the backbone of every outreach campaign. But the prettiest-looking designs and best-written emails can have hidden problems: messy HTML, broken links, spammy language or formatting that falls apart on mobile. These little errors can have huge implications—resulting in your emails not getting delivered, or being unreadable if they are. That’s precisely why an email template checker should be in your email workflow. In this post, we’ll break down what a template checker does, the common template mistakes it catches, and how these issues can silently undermine your entire campaign. You’ll also see how Warmy. io’s template checker can repair these fast – not technologies required– so your emails deliver, look great, reach more and perform better. What is an email template checker? An email template checker is an application that checks and verifies your email templates for problems that can negatively impact your deliverability. It serves like a quality control step, catching issues before your campaign goes live and gets reported as spam. At its core, a template checker analyzes the underlying structure and content of your email. It looks for issues like:Broken or outdated HTML codeMissing alt text for imagesInconsistent formattingUse of spam trigger wordsMobile and desktop rendering problemsThe goal? To ensure your email looks... --- > It's that time of day where you open your email marketing platform's dashboard to check the numbers. Your open rates are unexpectedly low. - Published: 2025-05-28 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/spf-dkim-and-dmarc-what-they-are-and-why-you-should-care/ - Categories: Blog - Tags: Marketing Imagine this: It's that time of day where you open your email marketing platform's dashboard to check the numbers. You see your open rates are unexpectedly low. Some recipients report that your emails landed in their spam folders—or worse, never arrived at all. Picture this: You open the dashboard of your email marketing platform and take a look at the numbers. And then you notice your open rates are lower than you would have hoped. Some recipients even say your emails got sent to spam—or even worse, never arrived. You run an email deliverability test and see your spam rates shooting up. You begin to wonder: Is my email system busted? Am I being blocked? Among the leading causes for this frustration is an error in email authentication. Without robust authentication, internet service providers (ISPs) and email providers have no way of knowing if your email is really from you. This could expose your domain to spoofing, phishing and deliverability problems. However, even legitimate senders and emails can get blocked or rerouted to spam end up blocked or diverted to spam if these authentication protocols aren’t configured as they should be. That’s why you want your bases covered, so you can make sure your emails land in inboxes. Understanding email authentication protocolsEmail authentication is the mechanism that checks if an email does, in fact, originate from the sender or domain it says to be. It’s akin to a security check for your messages, intended to protect senders and recipients alike. When you send... --- > You've set up your workflows and sequences to be as detailed as possible—taking into account all possible behaviors - Published: 2025-05-27 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/5-warning-signs-your-email-deliverability-is-suffering/ - Categories: Blog - Tags: Email Deliverability You spend so much time brainstorming and executing the most creative email campaign you've done to date. You've set up your workflows and sequences to be as detailed as possible—taking into account all possible behaviors of your target audience. But you're not getting the results you want. To make matters worse, you find out from a free deliverability test that most of your emails actually land in the spam folder instead. But what exactly went wrong? The success of your email marketing campaign could come down to email deliverability. You may be creating brilliant content and honing in on an ideal target market. But if your emails aren't being delivered to the inbox, your campaign results will be put to waste. Instead, your emails might be disappearing into spam folders or being blocked entirely without your even realizing it. This guide will walk you through the top five signs that your email deliverability is in danger. By catching these indicators early, you can act before your email marketing really suffers. Read on to see how you can identify these red flags and what you can do about them—plus a key resource that can help you diagnose and resolve your deliverability woes right away. Warning sign #1: Declining open rates (When your emails go missing in action)Let’s start by addressing the most common telltale signs that your email deliverability is struggling: a sudden decrease in open rates. Open rates are a a strong indicator of how interested your audience is, but most importantly,... --- > The subject is attention-getting, the design is beautiful and your offer…? Spot on. You hit send, you wait … and then comes the letdown - Published: 2025-05-27 - Modified: 2025-05-27 - URL: https://www.warmy.io/blog/why-your-emails-arent-reaching-inboxes/ - Categories: Blog - Tags: Email Deliverability When emails vanish, the outrage is understandable. You've spent hours putting together the perfect email. The subject is attention-getting, the design is beautiful and your offer... ? Spot on. You hit send, you wait ... and then comes the letdown. Open rates are down. Responses are nowhere to be found. Some contacts even say they found your message languishing in their spam folder. Sound familiar? If you’re nodding along, you’re not alone. Email deliverability problems are all too common—and incredibly annoying. No matter if you’re launching a new sales campaign, or a nurture sequence, or an update to your product, it's all for naught if your emails never make it into the inboxes of your audience. You'll miss out on the $36 for every $1 spent ROI. The good news? You can take control of this. And no, you don’t need to be an email tech wizard to solve the problem. Let’s dive in and get your emails back where they belong: front and center in the inbox. What is email deliverability and why does it matter more than you think? Let’s clear something up first: The fact that an email is sent does not mean it ends up in the inbox. Email deliverability is ability of your emails to arrive at the inbox of recipients. Not the spam folder, not the promotions tab, and certainly not the black hole. There’s a huge difference between email delivery and email deliverability:Delivery means the email has been accepted by the recipient’s server. Deliverability means the email actually landed in... --- > Email is without a doubt an insanely effective tool when it comes to marketing your business. Among email providers - Published: 2025-05-26 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/best-email-warm-up-tools-for-gmail/ - Categories: Blog - Tags: Email Deliverability Email is without a doubt an insanely effective tool when it comes to marketing your business. Among email providers, Gmail stands out with over 1. 8 billion active users globally. In the United States, Gmail holds a dominant 75. 78% market share, equating to roughly 130. 9 million users. These numbers reveal that many of your prospects and customers are probably using Gmail. However, reaching their inbox is not always straightforward. There are a lot of things that can happen from the moment you hit “Send. ” The spam filters and deliverability requirements in Gmail can send your emails to spam or the promotions tab. From a business perspective, especially small companies, freelancers, and eCommerce brands, poor deliverability when it comes to Gmail can mean missed opportunities, poor email engagement, and revenue left on the table. The importance of email warm-up for Gmail deliverabilityUsing Gmail as part of an email outreach strategy is super-important in order to maintain the best possible deliverability rates. You want to make sure your emails are as visible as possible, and are landing in inboxes instead of the spam folder or the promotions tab. Email warm-up has a lot to do with this cycle because it allows you to earn a positive reputation with email providers so that your IP will not get blacklisted and your emails will not be sent to spam. Gmail uses advanced spam filters which are backed by machine learning to recognize different signals related to sender reputation, email content, and user engagement... --- > Email is a critical communication tool for recruitment and HR teams—whether you’re contacting candidates, following up on job - Published: 2025-05-26 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/email-deliverability-benchmarks-for-recruitment-hr/ - Categories: Blog - Tags: Marketing Email is a critical communication tool for recruitment and HR teams—whether you’re contacting candidates, following up on job offers or sending internal communications to your employees. But if your emails are not getting to who you need to get them, then you’ve wasted all of that time and energy creating them. Bad email deliverability can spell disaster for recruitment efforts. From the promising candidates whose outreach copy ended up in the spam folder, to the internal memo that didn’t make it to your HR team on time. In this blog, we’ll dive into key email deliverability benchmarks that recruitment and HR teams should track. You’ll learn why these metrics are critical to your campaigns’ success and where you stand. We’ll also cover best practices and strategies that can help improve your email performance, from email warm-up tools to compliance best practices. Benefits of email marketing for recruitment and HRAccording to Beamery, a candidate is 5x more likely to see a message if it's sent through email. Let's go over the benefits of email marketing for human resource professionals and recruiters:Cost-effective communicationUnlike other methods of recruiting, such as print ads, digital ads, or in-person job fairs, email outreach is a low-cost alternative that allows recruiters to reach thousands of candidates from different locations. HR teams can also use email to deliver internal updates to staff, saving time and resources. With an ROI of $36 per $1 spent, email marketing proves to generate results with less cost. Better engagement and trackingEmail campaigns make... --- > Cybersecurity companies work in an industry where trust, security, and compliance are everything. Emails must not only land in the inbox! - Published: 2025-05-26 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/how-long-does-it-take-to-warm-up-an-email-domain-for-cybersecurity/ - Categories: Blog - Tags: Marketing Email domain warm up is a necessary process for any business that’s planning to send emails at scale and it’s even more crucial in the cybersecurity space. Cybersecurity companies work in an industry where trust, security, and compliance are everything. It isn't only about getting to see a $36 return for every $1 worth of spend. Emails must not only land in the inbox, but they must breed trust and reflect the credibility of that organization. The cybersecurity environment makes domain warmup a bit more challenging than it was before. Filters are getting more sophisticated, people are slightly more wary of the emails they receive. and you have to have a clean sending reputation in order to avoid suspicion of phishing or spoofing. This article will break down how long it typically takes to warm up an email domain for cybersecurity companies, generally between two to six weeks. We will cover best practices tailored for this sector, discuss common pitfalls, and show how tools like Warmy. io can streamline and secure your warm-up process. Why email domain warm-up is crucial for cybersecurity firmsWarming up your email domain is not only about the volume that you are sending. It is about building credibility and trust with both the inbox providers and your recipients. For cybersecurity companies, this holds more weight, as every message can be examined for security. Establishes trust with highly security-conscious recipientsIn this sector, more recipients are often more vigilant and suspicious—and with some very legitimate reasons to be. Given that 73% of... --- > Email marketing still reigns as one of the most powerful channels for nurturing prospects, leads, and customers for SaaS companies. - Published: 2025-05-26 - Modified: 2025-05-26 - URL: https://www.warmy.io/blog/best-email-marketing-platforms-for-saas-companies/ - Categories: Blog - Tags: Marketing Email marketing still reigns as one of the most powerful channels for nurturing prospects, leads, and customers for SaaS companies. The fact that more than 70% of marketers say email is driving more engagement proves that email marketing is an effective tool when it comes to engaging SaaS customers. Whether you are sending onboarding emails, newsletters, or promotional offers, email makes it easy to talk to your users in a direct and inexpensive manner. But, in order to make it work and to stand out in an increasingly crowded marketplace, it’s important to use the right email marketing platform. Since SaaS businesses are predominantly digital communicators, the platform you choose will make or break these wins. The right email marketing platform can implement gains on growth, engagement, and retention. Offering automation tools to run campaigns, personalized content and analytics for campaign performance, these platforms can help SaaS companies to optimize their email communication, and scale with efficiency. In this blog, we’ll look at how email marketing platforms help SaaS companies grow and retain business, what features are key for your business, and what platforms rise to the top of the market. We’ll also provide you with important insights into what you should look for in the platform that fits your specific needs. How email marketing platforms drive SaaS growth and retentionWith these systems, SaaS companies can automate, maximize, and measure email campaigns to connect with customers throughout their lifecycle—from sign­-up to renewal. Below, we explore how key email marketing strategies can directly contribute to SaaS growth... --- > Email is essential for fintech businesses when it comes to communicating with prospects, customers, and partners. - Published: 2025-05-23 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/how-long-does-it-take-to-warm-up-an-email-domain-for-fintech-companies/ - Categories: Blog - Tags: Email Deliverability Email is essential for fintech businesses when it comes to communicating with prospects, customers, and partners. In addition to being a deeply niche industry, fintech also comes with the responsibility of handling private user information. Therefore, trust and credibility are, above all else, significant. If you’re a fintech company with cold outreach campaigns or transactional messages, you’ll want to make sure you have a good sender reputation. In order to achieve this, you’ll need to warm up new email domains to ensure that you can build trust with inbox providers which will help in your deliverability rates. However, fintech companies face unique challenges when warming up a domain. The industry is highly regulated, financial communications are sensitive, and spam filters are becoming increasingly sophisticated, so starting off too hot or too fast will lead to your emails landing in spam or being blocked for good. In this article, we’ll discuss the amount of time it typically takes for a fintech to warm up a new email domain—usually, anywhere from two to six weeks—and why this time frame is paramount. We’ll also share best practices tailored for the fintech sector so you can get started right away. Why domain warm-up is critical for fintech companiesThe high ROI of email marketing ($38 return for every $1 spent) is not the only reason why this is a must-have channel for fintech companies. For fintech, email is vital, as it allows for one-to-one direct communication—required for dealing with sensitive information. Domain warm-up is more than just a... --- > For marketing agencies sending email campaigns at volume, there are key metrics that matter, when it comes to understanding deliverability - Published: 2025-05-23 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/email-deliverability-benchmarks-for-marketing-agencies/ - Categories: Blog - Tags: Marketing For marketing agencies sending email campaigns at volume, there are a few key metrics that matter most, when it comes to understanding deliverability. It doesn’t matter how good or targeted your campaigns are if your messages don’t even land in your client’s customer inboxes. Because when you have poor deliverability, you’re losing money—and you’re letting your clients down. These email deliverability benchmarks will give you some insight into how your agency stacks up with the rest of the industry. By knowing typical inbox placement rates, bounce rates, complaint rates, and spam trap hits, you can easily identify areas that have potential and areas that need to be revisited. Benchmarks also allow you to define realistic goals, uncover problems, and make the necessary improvements to achieve the highest possible results. In this guide, you will learn about the current email deliverability benchmarks for marketing agencies. We’re also going to look at how B2B deliverability compares with B2C. Finally, we’ll provide some practical tips to help your agency outperform these benchmarks and keep a good sender reputation with all major email providers. Key email deliverability metrics every marketing agency should keep an eye onTo improve email campaign performance, marketing agencies must monitor several core deliverability metrics. These indicators reveal how well your emails are performing in reaching inboxes and how recipients respond. Understanding each metric and its benchmarks helps agencies diagnose issues and optimize campaigns effectively. Inbox placement rate across major providersInbox placement rate is the percentage of sent emails that land directly in the recipient’s... --- > But with Outlook’s aggressive spam filters and intricate security precautions, getting your emails delivered could be quite difficult. - Published: 2025-05-23 - Modified: 2025-05-23 - URL: https://www.warmy.io/blog/improve-email-deliverability-in-outlook/ - Categories: Blog - Tags: Email Deliverability Microsoft Outlook is used by over 400 million active email users around the world, and serves as one of the most popular email platforms for businesses and general consumers. But with Outlook’s aggressive spam filters and intricate security precautions, getting your emails delivered could be quite difficult. For businesses relying on Outlook to communicate with their customers, prospects or partners, having their emails delivered to the spam or junk folder means lost opportunities, lost revenue and damaged reputation. Microsoft 365’s usage has taken flight—with a particular spark among B2B SaaS companies and corporate sales teams). With an 8. 10% market share, getting your emails in Outlook inboxes is as high-stakes as it ever was. In this article, you will find tips and information on best-practice tactics you can use to improve your email deliverability in Outlook. We will help you deliver your email campaigns to that trusty contact’s Outlook inbox while optimizing the Outlook email campaign experience. Understanding Outlook’s spam filters and SmartScreenOutlook has sophisticated filtering mechanisms to keep its users protected against junk or harmful emails. These filters look at several signals to determine if an email should land in the inbox, junk folder, or be completely blocked. At the heart of this is Microsoft’s SmartScreen filter, which is used along with more traditional spam-detection tactics. By understanding how these systems work and how user engagement can impact their decisions, you can increase your chances to deliver optimal deliverability rates with Outlook. How Outlook’s spam filter worksOutlook. com's junk filters look for several key indicators to determine... --- > In the SaaS landscape, success lies in nurturing leads and retaining customers. After all, the subscription business industry - Published: 2025-05-21 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/top-email-marketing-tips-for-saas-companies/ - Categories: Blog - Tags: Email Deliverability In the SaaS landscape, success lies in nurturing leads and retaining customers. After all, the subscription business industry follows the recurring revenue model—with the MRR (monthly recurring revenue) as the indicator of growth. But in a crowded field of SaaS companies, standing out requires more than generic marketing. It requires strategic, data-driven campaigns based on an understanding of your audience’s needs. Email marketing fills that gap, and is one of the most effective ways to affect those variables. In this guide, we’ll share concrete email marketing tips tailored for SaaS businesses. From segmentation and personalization to drip campaigns and deliverability best practices, these strategies will help your team create engaging, results-driven campaigns. Ready to take your SaaS email marketing strategies to the next level and achieve some real growth? Let’s dive in. Why email marketing is not optional for SaaS companiesThe global SaaS market is projected to generate almost $819 billion by 2029, showing that the potential for growth is immense. Unlike many other digital channels, an email campaign offers a direct, personal line of communication with users throughout their entire customer journey. It’s can be used to reach your users at every touchpoint—both for new users you are attracting, existing subscribers, and returning users who need more value from your product. An effective email marketing strategy will increase your trial-to-paid conversions, lower your churn, and increase lifetime value per customer. It boasts one of the most favorable ROIs of digital channels, so it’s essential in any SaaS marketer’s arsenal. Ignoring or downplaying... --- > When it comes to marketing agencies, email is not just a tool for communication, it’s the horse that pulls client email outreach - Published: 2025-05-21 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/how-long-does-it-take-to-warm-up-an-email-domain-for-marketing-agencies/ - Categories: Blog - Tags: Email Deliverability When it comes to marketing agencies, email is not just a tool for communication, it’s the horse that pulls client email outreach, campaign success, and lead generation—both for the agency and its clients. After all, email marketing's ROI is $36 per $1 spent. It's understandable for agencies and their clients to want a piece of that. But perfectly crafted campaigns can still fail if the emails don’t make it into the inbox. That’s where email warm-up comes in. For agencies who are working with multiple clients, each with their email domains, and objectives for outreach, warming up can feel like a shotgun approach. How long does it really take? What steps should you follow? And how do you do it safely and efficiently across accounts? In this post, we’re going to dissect the standard warm-up schedule, what influences how fast (or slow) you can do it successfully, and best practices for marketing agencies. So whether you’re bringing a new client on board or scaling up a high-volume outreach operation, this guide will help you ensure you don’t make rookie mistakes. It's high time for you to develop a sender reputation that works over time for you (not against you) and enjoy long-term success. Why warming up an email domain matters for marketing agenciesWhen you properly warm up your email, it is the practice of establishing a positive reputation for sending mail with mailbox providers like Gmail, Outlook, and Yahoo by slowly increasing message volumes over a period of 30 to 60 days.... --- > In the fast-moving world of ecommerce, competition can be tough. With the market revenue expected to reach US 4.32 trillion in 2025 - Published: 2025-05-21 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/top-email-marketing-tips-for-ecommerce-platforms/ - Categories: Blog - Tags: Email Deliverability In the fast-moving world of ecommerce, competition can be tough. With the market revenue expected to reach US 4. 32 trillion in 2025, the numbers speak for themselves. Ecommerce is here to stay. It's already a huge part of people's everyday lives. If you’re trying to sell more and increase customer lifetime value for your ecommerce store, having an email marketing program is essential. Email marketing offers the highest return on investment of any digital channel, so it’s not surprising businesses invest a good amount in it. In this guide we are going to share email marketing tips that will enable ecommerce businesses to grow and scale. From better understanding customer segmentation and writing mouth-watering cart abandonment emails to making the most out of automation and A/B testing, these few simple strategies will let your store’s sales potential out of its cage. Are you ready to take your email marketing to the next level and experience real, measurable growth for your online store? If so, you’re in the right place. Why email marketing is essential for ecommerce businessesHere are several advantages that contribute to making email marketing one of the most effective marketing channel for ecommerce companies:A direct line to your customers: Email allows you to get your message directly in front of a shopper (in their inbox) without having to fight social media algorithms or pay for them to see your ad. Gives a high ROI (Return on Investment): For every $1 spent on email marketing, you can earn an average of $36 in return.... --- > In the UK alone, 8.3 billion (as of April 2024) emails are sent each day, opening up vast potential for business growth. - Published: 2025-05-21 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/how-to-increase-email-deliverability-in-the-uk-market/ - Categories: Blog - Tags: Email Deliverability Breaking into the UK market with email campaigns is both challenging and rewarding. There are many variables at work in the situation—regional ISPs, UK laws and even a few cultural quirks. In the UK alone, 8. 3 billion (as of April 2024) emails are sent each day, opening up vast potential for business growth. But a one-size-fits-all email plan won’t cut it. So what works in the US to get your email delivered, may not be so successful in the UK. If tactics fail, your brand reputation could take a hit—and those emails could find themselves in spam. What we mean by this is basically: if you want to succeed in email marketing in the UK, it's crucial to customize your approach. It must align with UK's technical requirements, legal landscape, and even audience behavior. In this guide, we’ll explore steps designed to help you increase email deliverability in the UK. Understanding the UK email ecosystemBefore we jump right into specific deliverability tactics, let’s take a look at what makes the UK email ecosystem different. GDPR, privacy, and consentSince Brexit, the UK has maintained its own version of the General Data Protection Regulation known as the UK GDPR. This outlines what businesses do with personal data, such as email addresses or an email list, when they’re collected and stored. Compliance with the UK GDPR is not optional. Not complying could lead to fines and damage to your brand if punished. Perhaps the most critical element of UK GDPR is securing consent using ‘opt-in’ before you start... --- > Gmail's spam abyss is much like the internet's black hole—where your carefully crafted emails vanish. Well, you're not alone. - Published: 2025-05-19 - Modified: 2025-05-19 - URL: https://www.warmy.io/blog/improve-email-deliverability-in-gmail/ - Categories: Blog - Tags: Email Deliverability Gmail's spam abyss is much like the internet's black hole—where your carefully crafted emails vanish. Well, you're not alone. Sending emails that end up ignored by recipients is one thing. But sending emails that don't even land in inboxes? It can feel like trying to get your dog or cat to take a bath—frustrating and nearly impossible. But don't worry—improving your Gmail deliverability is definitely possible. No magic tricks needed. With just the right technical setup and deliverability strategies, you can improve email deliverability in Gmail soon. This guide will walk you through everything you need to know to get Gmail to see you as a reputable sender. From setting up SPF, DKIM, and DMARC to warming up your email and crafting content that avoids the dreaded spam folder, you’ll get practical, easy-to-follow tips. Introduction to email deliverability in GmailIt goes without saying that Gmail is one of the most powerful platforms in the world. With a 75. 78% market share in the United States alone, Gmail no doubt serves billions of users everyday. Because of its role in helping marketing and sales teams all over the world, Gmail has developed strong internal systems to protect its users from spam and the dangers of the internet. For email senders, Gmail's deliverability is a must. It can be the key to ensuring your emails land where they're supposed to be. If your emails don’t reach Gmail inboxes, you risk losing a huge portion of your audience and potential revenue. Here's a... --- > With a $36 return on every $1 spent, email marketing is a valuable tool for businesses to interact with customers and increase sales - Published: 2025-05-19 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/email-marketing-compliance-checklist-for-us-market/ - Categories: Blog - Tags: Email Deliverability With a $36 return on every $1 spent, email marketing is a valuable tool for businesses to interact with potential customers and increase sales. Meanwhile, companies in the US will be happy to learn that the US was the country with the most emails sent in April 2024—with an average of 9. 7 billion emails sent each day. However, this is easier said than done. The spam folder is where many businesses go to die. There are a lot of different things that contribute to this—content, engagement, reputation, for example—but one of the things that compliance can do is help build your foundation on the way to email marketing success. The US has laws that tightly govern what and how businesses can market through email. It’s not an option to flout these rules, if you’re interested in keeping your brand’s reputation intact and your emails delivered to the inboxes of your audience. This marketer’s compliance checklist includes the major legal requirements for email marketing. Using this checklist will ensure your email campaigns are respectful to your subscribers, legal, and more effective in your marketing. The consequences of non-complianceWhat happens if you fail to comply with US email marketing laws? There may be serious consequences, such as:Potential fines and legal action. There may be hefty fines and penalties per non-compliant email. Beyond financial consequences, legal action from recipients can also incur additional costs and business disruption. Brand reputation damage. Non-compliance essentially shows disrespect for rules of the law. This destroys trust and may lead... --- > When it comes to email outreach, getting your emails into the primary inbox—not spam or promotions—is everything - Published: 2025-05-16 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/free-vs-paid-email-warm-up-tools-which-is-best/ - Categories: Blog - Tags: Marketing When it comes to email outreach, getting your emails into the primary inbox—not spam or promotions—is everything. A lot rides on your emails landing in your target inboxes, and one of the most critical steps in achieving this is properly warming up your email address before you go all out in launching campaigns. Whether you're a solo founder or a scaling sales team, or whatever stage of growing your business you're in, this remains a fact: email warm-up tools play a big role in helping you build a strong sender reputation and improving email deliverability. Once you start exploring tools though, you'll likely have this thought crossing your mind: "Do I go with a free tool or invest in a paid email warmup tool? " Now, you're probably here because you're confused. You might be weighing the pros and cons and doing a wee bit of research. Well, this guide explores the key differences between free and paid email warm-up tools. We’ve broken down the pros and cons of each option to help you decide what course to take. What are email warm-up tools? Email warm-up tools are software solutions that can help improve the reputation of your email address and domain with email service providers (ESPs) like Gmail, Outlook, and others. These tools work by sending a series of carefully crafted emails back and forth with real or simulated recipients—mimicking natural email behavior. These behavioral patterns then send signals to various ESPs which they use as basis to determine... --- > If you're sending cold emails for your SaaS company, you probably spend a lot of time crafting really great copy - Published: 2025-05-15 - Modified: 2025-05-15 - URL: https://www.warmy.io/blog/how-long-does-it-take-to-warm-up-an-email-domain-for-saas-companies/ - Categories: Blog - Tags: Email Deliverability If you're sending cold emails for your SaaS company, you probably spend a lot of time crafting really great copy and setting up comprehensive workflows. You also probably look at your numbers often—your open rates, click-through rates, revenue from email, leads generated, etc. Now don't get us wrong. These are all very important and essential parts of an email marketing strategy. We just have some questions for you—is your email domain warm enough? Is your email domain set up for success? For SaaS firms using email outreach to drive leads and communicate, warming up your email domain is the first step to making sure these messages reach the inbox (and not the horrible spam folder). Even if the content is entertaining and relevant, if you don’t warm up, your best emails will land in the spam folder and damage your reputation. "Email warm-up" refers to the practice of slowly ramping up the volume of email sent from a new, or underused, domain in order to establish favorable sender reputation with email service providers. This will make it harder for your emails to be marked as spam and improve deliverability in the long run. Basically, the warmer a domain is, the better chances that their cold emails will reach the inbox. Why warming up an email domain is crucialMany SaaS businesses allot a low budget for email marketing compared to other marketing efforts. However, the ROI on email marketing is a skyrocketing 201%. What does this mean? Warming up your email domain is essential... --- > Learning the intricacies of email deliverability to US contacts is a must for global marketing teams, SDRs, and agencies - Published: 2025-05-15 - Modified: 2025-05-15 - URL: https://www.warmy.io/blog/how-to-increase-email-deliverability-in-the-us-market/ - Categories: Blog - Tags: Email Deliverability Email delivery is an important ingredient in the success of any email marketing campaign. But it can get very complicated when it comes to reaching prospects in the United States. Learning the intricacies of email deliverability to US contacts is a must for global marketing teams, SDRs, and agencies selling to America, though. In this guide, we are going to dive into the tactics, regulations, and best practices you need to know about if you want better email deliverability in the US. Whether you are a company operating outside the US and want to expand your business, or a sales team in the region who wishes to optimize your cold email campaign—these tips and insights will be your guide. Read on to discover how you can enhance your email success in the US market and get your messages exactly where they belong—into your recipients’ inboxes. Understanding the US email landscapeEmail deliverability in the United States is critical for any business aiming to succeed. In April 2024, the US market had the highest volume of emails exchanged—that means an average of 9. 7 billion emails sent daily. This shows how competitive the digital environment is. Aside from the market being competitive, businesses also struggle with inbox placement. A recent study by the Warmy Research Team, titled Mastering Global Email Deliverability in 2024–2025 reports that the average inbox placement rate for North America is around 85%. This means that even in an established market, around 15% of emails still fail to reach the... --- > Emails are an integral part of digital marketing. However, even the most beautifully-written emails end up in the spam holder - Published: 2025-05-15 - Modified: 2025-08-07 - URL: https://www.warmy.io/blog/why-your-emails-land-in-spam-deliverability-tips/ - Categories: Blog - Tags: Email Deliverability Emails are an integral part of digital marketing. However, even the most beautifully-written emails end up in the spam holder—the black hole of emails. It's a frustrating issue that many marketers face no matter how much they try. So what’s with all these emails getting rerouted to the spam folder? And, worst of all, what can you do to stop it? These are the two questions this article seeks to address. How does ending up in the spam folder impact your business? The ramifications of poor deliverability can be severe and can impact anything from customer confidence to your revenue. Reduced engagement and sales. If your emails go to spam, no one reads them. This makes it hard for people to see your emails, which means less opens, less clicks, and less conversions. So if you use email marketing to drive sales or nurture leads, this can have an immediate impact on your revenue. Damage to your sender reputation. Your sender reputation is crucial for inbox placement. If you find that your emails are repeatedly being labeled as spam, email service providers (ESPs) will view your domain as untrustworthy. This can cause even more of your emails in the future to end up in spam, and it becomes a vicious cycle. Impact on deliverability across other channels. A poor reputation in one channel can have a ripple effect. Dissatisfaction in one channel can have negative spillover effects. If major ESPs start flagging your emails, it may affect who you’re able to reach on other platforms. So if you’re... --- > In 2025, email service providers ESPs have leveled up when it comes to security and strict spam filtering mechanisms. - Published: 2025-05-14 - Modified: 2025-05-14 - URL: https://www.warmy.io/blog/email-warm-up-checklist-for-new-domains-in-2025/ - Categories: Blog - Tags: Email Deliverability Marketers with email campaigns in their toolbox know all too well that to be successful, it's essential to launch a new domain—which is exciting. But if you start sending too many emails right away, they might just end up in the spam folder. In 2025, email service providers (ESPs) have leveled up when it comes to security and strict spam filtering mechanisms. There's no other way around it but to do it the right way: by warming up your domain before launching your first campaign or cold email. If you're a SaaS startup, eCommerce brand marketer, or B2B marketer, you're in the right place. This blog is your step-by-step email warm-up checklist for new domains in 2025. We will walk you through every stage. You’ll learn how to prepare your domain, what to monitor, how to scale safely, and how tools like Warmy. io can automate the process with fewer risks. Let’s make sure your domain starts strong—and stays out of the spam folder. Why email warm-up matters for new domainsBefore we discuss why warmup matters for new domains when it comes to email marketing, we need to answer one frequently asked question. Q: Why do you need a new domain for outreach in the first place? A: Using your primary business domain (the one your website and customer communications are already built on) for cold outreach is risky. If your outreach campaigns trigger spam complaints, high bounce rates, or poor engagement, your domain reputation can take a hit. Inbox... --- > In the world of email deliverability, most senders obsess over one moment: the first send. Will it land in the inbox or spiral into spam? - Published: 2025-05-09 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/thread-or-dread-gsuite-vs-ms365-in-follow-up-deliverability/ - Categories: Blog - Tags: Industry insights In the world of email deliverability, most senders obsess over one moment: the first send. Will it land in the inbox or spiral into spam? But what if that moment matters far more than we ever realized? At Warmy. io, we set out to explore a critical but overlooked question: Does the inbox placement of your first email (regardless of content, timing, or format) determine the fate of all follow-ups in the same thread? And more importantly, does this behavior differ between major platforms like GSuite and MS365? The findings surprised even our seasoned deliverability experts. This blog breaks down our latest research, testing conditions, platform-specific quirks, and—most importantly—what it means for your campaigns moving forward. Whether you’re running cold outreach, lead nurturing, or customer onboarding sequences, this report will help you understand why the first message in your thread isn’t just the first impression—it’s the whole game. Behind the scenes: how we engineered the inbox experiment“Can a successful first email guarantee smooth inbox placement for all follow-ups? ”“Does the initial inbox placement lock in thread behavior—or can follow-ups shift the outcome? ” These were the main questions Warmy’s Research Team sought to answer. To understand how email threads behave after the first message lands, we needed more than assumptions—we needed structured, platform-specific experimentation. Q: What are email threads? A: Email threads are a series of connected messages exchanged between participants, where each subsequent email is grouped under the original message, maintaining continuity in the conversation. They help keep related... --- > Whether you are running cold outreach, nurturing leads, or sending out transactional updates, bounced emails are an annoyance - Published: 2025-05-05 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/its-time-to-bounce-back-esp-specific-strategies-that-actually-work/ - Categories: Blog - Tags: Industry insights Whether you are running cold outreach, nurturing leads, or sending out transactional updates, bounced emails are an annoyance—and more than that, they signal that something is wrong. At Warmy. io, we’ve been running controlled deliverability experiments across major email service providers (ESPs)—Gmail, Outlook/MS365, Yahoo, AOL, and Zoho—to understand exactly why emails bounce, what those bounce codes actually mean, and how to fix the underlying issues. This blog post focuses on hard vs. soft bounce root causes, real-world thresholds, and remediation strategies you can actually use—especially if you're battling rejections, spam folder traps, or silent greylisting. Bounce basics: hard vs. soft bouncesBefore diving into provider-specific insights, it’s important to understand the two core types of email bounces:Hard-bounce: Invalid addresses Spam or email rejection DMARC failureSoft Bounces: Full mailbox Greylisting Temporary server issueWhat are hard bounces? These are permanent failures which come with a 5xx error message. Your email is rejected and won’t be retried. Common causes include:Nonexistent email addresses (e. g. , typos or abandoned inboxes)Failing SPF, DKIM, or DMARC checksIP/domain blacklistingContent flagged as spam or violating ISP policyRelated Reading: Fixing 550 Permanent Failure for One or More Recipients: A Complete GuideWhat are soft bounces? These are temporary issues with 4xx codes. Your email didn’t go through, but the server may try again. Common causes include:Greylisting (a spam control tactic that delays unknown senders)Recipient’s mailbox is fullServer is busy or temporarily unavailableVolume-based throttling or rate limitsSoft bounces are often an early warning. If ignored, they can snowball into permanent failures. A... --- > As businesses expand their reach beyond borders, making sure that emails are received and land in people's inboxes becomes vital - Published: 2025-04-28 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/mastering-global-email-deliverability-in-2024-2025/ - Categories: Blog - Tags: Industry insights In today’s interconnected world, email as a communication channel is a double-edged sword. It’s easy, quick and allows businesses to connect with multiple clients at the same time. But some specific sending behavior combined with other technical factors can lead businesses to be labeled as questionable--not a great result for a worldwide business. Thus, worldwide email deliverability is critically important to any company using email marketing efforts. As businesses expand their reach beyond borders, making sure that emails are received and land in people's inboxes becomes vital. Because let’s face it. Good deliverability rates mean better engagement, higher conversions and better business results! However, email deliverability is not a one-size-fits-all concept. Each region faces unique challenges and understanding these regional differences is essential to achieve strong inbox placement at a global level. This article draws from a recent report by the Warmy Research Team. It contains a deep dive into how infrastructure, ISP policies, regulations, engagement norms, and blacklist practices impact deliverability across various regions (North America, EMEA, APAC, and Latin America). If you’re at the helm of a business looking to expand globally with email as a key communication channel, you will want to read on. Different regions, different deliverability: Dissecting this phenomenonEmail deliverability varies greatly across regions, and there are many factors that influence this: infrastructure and ISP policies; regulations and compliance issues; user engagement and cultural norms; utilization of spam traps and blacklists. Local infrastructure & ISP policies vary due to different advancements in technologyKey observations include:Local and regional... --- > Discover how email blacklists affect your deliverability and learn how to avoid getting flagged by major email providers. - Published: 2025-04-22 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/are-blacklists-killing-your-emails-a-deep-dive-into-how-they-influence-email-providers/ - Categories: Blog - Tags: Industry insights In 2025, email remains one of the best ways to reach prospects and customers. But deliverability isn't guaranteed—especially if your domain or IP lands on a third-party spam blacklist. These DNS-based blocklists (DNSBLs) are maintained by anti-spam organizations and used by email providers to filter out unwanted messages. For senders, being listed in even one major blacklist can result in blocked messages, spam-folder placement, or throttled delivery. This guide is based on an in-depth report by the Warmy Research Team with the goal of uncovering how different mailbox providers use third-party blacklists in practice—not just theory. If you’re serious about improving your sender reputation and maximizing email performance, this report is your roadmap. What are third-party email blacklists (DNSBLs)? Third-party email blacklists or DNSBLs track IP addresses and domains known for sending spam or demonstrating abusive or suspicious email behavior. When you send an email, the receiving server may query one or more DNSBLs in real time. If your sending IP or domain appears on a list, the server may immediately reject the message (hard bounce), route it to the spam folder, or apply stricter filtering. Blacklists don’t all function the same way—some are highly reputable and used globally, while others are aggressive, pay-to-delist, or known for high false-positive rates. At the same time, email service providers use blacklists differently. Email service providers like Google Workspace, Gmail, Microsoft 365, Outlook, and Yahoo also have their own spam-filtering mechanisms. Understanding which blacklists matter to which providers is key to maintaining inbox... --- > Email deliverability—crucial yet often elusive goal for businesses aiming to connect with their audience. But there’s a harsh reality - Published: 2025-04-14 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/how-to-avoid-email-blocks-lessons-from-ms365s-deliverability-research/ - Categories: Blog - Tags: Industry insights Email deliverability—crucial yet often elusive goal for businesses aiming to connect with their audience. But there’s a harsh reality: As good as your content is and as personalized as your outreach is, if your emails don’t reach that inbox, they just don’t work. In a time when inboxes are bombarded with spam and unwanted emails, it’s essential to ensure your emails are received in the first place. Yet, maintaining high deliverability rates is complicated. Plus, it is influenced by numerous factors like sender reputation, email content, and sending patterns. These challenges are even more pronounced for businesses that use Microsoft 365 (MS365) as their email service provider (ESP). MS365 is a prevalent email provider used by many organizations, but its relatively strict filtering mechanisms means that even legitimate outreach can often be mistakenly flagged as spamThis research dives into the intricacies of email deliverability for MS365 sender accounts. Specifically, it examines how controlled warmup strategies—gradually increasing email volume and varying content formats—affect the performance of MS365 as a sender when targeting major email providers like Gmail and GSuite. The findings from this study provide valuable insights into the best practices for improving email outreach, preventing blocks, and optimizing sender reputation for higher inbox placement rates. f Research methodology: How we tested MS365's deliverabilityTo gain deeper insights into the intricacies of MS365’s email deliverability, we conducted a series of controlled experiments. These tests were designed to evaluate the impact of different sending volumes, content formats, and provider-specific factors on inbox placement.... --- > Welcome to the new email landscape where email deliverability has never been more important. With inbox providers tightening their rules - Published: 2025-04-07 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/the-email-deliverability-playbook-5-key-trends-that-will-define-inbox-success-in-2025/ - Categories: Blog - Tags: Industry insights Welcome to the new email landscape where email deliverability has never been more important—or more complex. With inbox providers tightening their rules, AI-driven filters evolving fast, and new privacy laws rolling out across the globe, what worked last year simply won’t cut it in 2025. The Warmy. io Research Team created this guide: to give Warmy users a clear, actionable overview of the most important deliverability trends for the year ahead. Whether you’re a solo founder or managing campaigns at scale, these insights will help you stay compliant, land in the inbox, and get the results you need. Key trend #1: Authentication or oblivion—why SPF, DKIM & DMARC are now non-negotiableEmail authentication is no longer a nice-to-have—it’s the baseline requirement for anyone who wants to land in the inbox in 2025. Q: What are SPF, DKIM, and DMARC and why are they relevant for deliverability? A: This “email trinity” is a set of email authentication protocols that verify whether an email is legitimately sent from your domain. They help protect against spoofing and phishing, and are essential for building trust with inbox providers. Without them, your emails are more likely to land in spam or be rejected entirely. Related Reading: SPF, DKIM, and DMARC: Boosting Email Security and DeliverabilityWhat's changed in 2025? In early 2024, Google and Yahoo began enforcing strict authentication requirements for high-volume senders (those sending more than 5,000 emails/day). Now, Microsoft has followed suit, announcing similar rules for all bulk senders starting May 5, 2025. What does... --- > In this guide, we’ll walk you through what causes SMTP Error 451 4.4.2, how to troubleshoot and fix it - Published: 2025-04-02 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-451-4-4-2-bad-connection-to-remote-mail-server-causes-fixes/ - Categories: Blog - Tags: Email Deliverability You’ve just sent a high-stakes email to a potential client, pressed send, and anxiously waited for the response that could yield a big contract. But instead of that response showing up in your inbox, you receive an ominous message: SMTP Error 451 4. 4. 2 – Bad Connection to Remote Mail Server. This error delays important communications and raises red flags about your email infrastructure, connectivity, and reputation. Luckily, this isn’t a dead-end situation. In this guide, we’ll walk you through what causes SMTP Error 451 4. 4. 2, how to troubleshoot and fix it, and most importantly, how you can take steps to prevent this disruption from happening in the future. What is SMTP Error 451 4. 4. 2? SMTP Error 451 4. 4. 2 is a transient error when a mail server has problems connecting to a remote mail server. This error message generally indicates that the server could not send the email because it couldn't connect properly to the mail server at the receiving end. What happens then is the email is not delivered right away and it remains pending in server’s queue. Most of the time, SMTP Error 451 4. 4. 2 doesn't signal a permanent issue but a temporary one. But if you ignore it and it stays unresolved, it can create delays, even worse—bounce-backs or rejections. So if you see this error, remember it’s not necessarily cause for panic. It’s simply a warning that your message had trouble getting through at the moment. Primary causes of SMTP Error... --- > If you’ve ever had to deal with the dreaded SMTP Error 502 5.5.1 – Command Not Implemented that occurs while attempting to send an email - Published: 2025-04-01 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-502-5-5-1-command-not-implemented-how-to-fix-it/ - Categories: Blog - Tags: Email Deliverability If you’ve ever had to deal with the dreaded SMTP Error 502 5. 5. 1 – Command Not Implemented that occurs while attempting to send an email, know that this is actually much more common than you might expect. Especially when you want to send out emails immediately, this error proves confusing (and frustrating) because it breaks your workflow and delays communication. So what does it actually mean? In simple terms, SMTP Error 502 5. 5. 1 basically means that the SMTP server you’re in communication with does not recognize or support a command your email client is attempting to send. This might be due to outdated software, misconfigured server settings, or unsupported authentication methods. The good news? It’s fixable. In this complete guide, we’ll explain exactly what the error means, its causes, how to troubleshoot it, and the fixes to get you emailing again. What is SMTP Error 502 5. 5. 1? SMTP Error 502 5. 5. 1 is an error message returned from the mail server of the mail client, informing the mail client that the mail server does not recognize or support an SMTP command. Now, let’s dissect the error code:502: Standard SMTP status code. You can explore other SMTP Errors with 502 code here. 5. 5. 1; Enhanced status code indicating a syntax or command issueThis typically happens during the initial handshake between the email client and the SMTP server. For example, your client might send commands like:EHLO: used to identify the client and request server capabilitiesAUTH: used to start the... --- > In this guide, we’re going to explain exactly what SMTP Error 421 4.3.0 means, why it happens, and how you can resolve it quickly. - Published: 2025-04-01 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-421-4-3-0-temporary-mail-server-error-causes-fixes/ - Categories: Blog - Tags: Email Deliverability You’re blasting out emails—perhaps a newsletter, an onboarding sequence, a sales drip—and you hit a wall. Your computer displays “SMTP Error 421 4. 3. 0. ”It’s a frustrating message that means your email didn’t go through. Even worse, it’s a bit vague. What does it really mean? Is something broken? Are your emails being blocked? The good news: it’s a temporary error. The bad news? Failing to address the underlying issue could lead to a cycle, and this repeated behavior can very well have a negative effect on your email deliverability in the long run. In this guide, we’re going to explain exactly what SMTP Error 421 4. 3. 0 means, why it happens, and how you can resolve it quickly. We guide you through solutions and ways to prevent it from happening on your server in the future, whether you're using your own mail server or an SMTP relay service. What is SMTP Error 421 4. 3. 0? SMTP Error 421 4. 3. 0 is a temporary issue that occurs when a mail server can’t process your email request at that moment. It doesn’t mean your message’s been outright rejected, but that the server’s too busy or lacking in resources to take it on at this moment in time. SMTP response codes fall into two main categories:Temporary errors (4. x. x): These are issues that are not permanent and can often be resolved after a short delay. Permanent errors (5. x. x): These indicate a failure that cannot be resolved by simply retrying.... --- > In the world of emails, getting your message seen is just as important as crafting the perfect copy. - Published: 2025-03-31 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/mastering-email-deliverability-the-modern-guide-to-authentication-and-inbox-warm-up/ - Categories: Blog - Tags: Industry insights In the world of emails, getting your message seen is just as important as crafting the perfect copy. But even the most well-written email is worthless if it never makes it to the inbox. That’s where email warm-up and authentication come into play—and why understanding their intersection is no longer optional. However, the email landscape continues to become even more complex. Security standards are tightening, legacy protocols are fading, and mailbox providers are smarter—and stricter—than ever. This means the rules around how emails are sent, authenticated, and received are shifting fast. This research report was born out of that complexity. It blends Warmy’s internal findings with official documentation and real-world email infrastructure trends to give you a clear, up-to-date view of what’s happening behind the scenes—and what you need to do to stay ahead. The premise: Understanding inbox warmup and email deliverabilityInbox warmup is the practice of gradually building trust with mailbox providers. Think of it like building credit. When you open a new bank account or get a new phone number, you don’t immediately start making large transactions or calling hundreds of people. You build a track record first. Warmup works the same way for email. By starting with low sending volumes and slowly increasing activity, your email address begins to appear more legitimate in the eyes of spam filters. A proper warmup process includes opening emails, replying to them, marking them as important, and even removing them from spam folders. These behaviors signal positive engagement, helping email providers... --- > It can feel like hitting a wall when you run into SMTP Error 555 5.5.2—and everything seems to be configured correctly. - Published: 2025-03-27 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-555-5-5-2-syntax-error-causes-fixes/ - Categories: Blog - Tags: Email Deliverability It can feel like hitting a wall when you run into SMTP Error 555 5. 5. 2—and everything seems to be configured correctly. So whether or not you happen to be a developer sending emails programmatically or an IT admin managing a mail server, this error can be a clear indicator that something is amiss at the protocol level. In this guide, we’ll decode the 555 5. 5. 2 error, show where it most commonly appears (like in logs or SMTP responses), and explain how mail servers interpret it. More importantly, you’ll receive actionable, practical fixes to get your emails flowing smoothly again—all without having to become a mail server wizard. What is SMTP Error 555 5. 5. 2? SMTP Error 555 5. 5. 2 is a syntax error that occurs during the email delivery process when a command, typically MAIL FROM or RCPT TO, is not properly formatted. It's a subset of SMTP Error 555. This error informs the sending server that the receiving mail server is unable to parse the command due to syntax error—often a malformed email address or some required formatting elements like angle brackets missing. “555” indicates a permanent failure, and “5. 5. 2” specifically means a syntax error in the SMTP conversation. From the viewpoint of a mail server, this error is a defensive tactic. It keeps malformed messages from entering the system, thereby assisting in guarding against spam, spoofing, and abuse. The receiving server expects specific SMTP command formats and will immediately reject anything that deviates from the... --- > If SMTP Error 421 4.7.27 lands in your lap, it’s a warning sign—a gentle reminder from the email gods to stop - Published: 2025-03-27 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-421-4-7-27-connection-rate-limited-causes-solutions/ - Categories: Blog - Tags: Email Deliverability A lot of email senders simply click 'send' without much thought. That’s because email has become routine—a feature of everyday life. But for email senders who rely on the channel for marketing or outreach use cases, a lot is happening behind the scenes. You write an irresistible subject line, you nail the content, and you’re ready to hit “Send. ” But instead of hitting your recipients’ inboxes, your emails bounce back with a cryptic message— SMTP Error 421 4. 7. 27 – Connection Rate Limited. What just happened? Why is your email server suddenly playing gatekeeper? If SMTP Error 421 4. 7. 27 lands in your lap, it’s a warning sign—a gentle reminder from the email gods to stop, slow down and play by the rules. In this guide, we’ll explain why this error occurs, how to resolve it, and best practice to help your emails be delivered without errors. What is SMTP Error 421 4. 7. 27? SMTP Error 421 4. 7. 27 – Connection Rate Limited is a response from an email server indicating that the sender has exceeded the permitted number of connections within a specific timeframe. This error isn’t a permanent rejection but a temporary speed bump in your email-sending highway. That means either your email server (or the recipient’s server) is hitting the brakes on your connection attempts. You’ve hit a rate limit, and your emails are being throttled before they can even land in an inbox. You’ve triggered a rate limit, and your emails are being throttled before they even... --- > This report is more than just an overview. It is carefully tailored to support Warmy users in maximizing their email deliverability - Published: 2025-03-25 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/understanding-esp-blocks-causes-types-and-prevention/ - Categories: Blog - Tags: Industry insights Predictions show that by 2027, there will be 408. 2 billion emails sent per day. What does this mean? It shows how big a role email has in everyday life. For businesses and individuals depending on email as primary means of communication, the ability to land in the inbox is everything. That being said, email deliverability is the unsung hero behind every successful campaign. However, amidst the hustle to craft the perfect email, most are blindsided by a common yet misunderstood hurdle—email blocks. These blocks can impede your efforts, sending your email to a temporary deferral status or a permanent spam folder placement—ultimately damaging your sender reputation. Warmy’s research team decided to take a deep dive into the inner workings of email blocks—causes, types, and prevention strategies. But this report is more than just an overview. It is carefully tailored to support Warmy users in maximizing their email deliverability. So whether you’re new to the concept or have experienced the frustration of blocked emails, this report will empower you with the knowledge to keep your outreach smooth, effective, and, most importantly—in the inbox. What are ESP blocks? Email Service Providers (ESPs) such as Gmail, Outlook, and G Suite (now Google Workspace) are at the core of controlling the emails that get to their users. They rely on sophisticated algorithms and filters to decide which emails get delivered to the inbox and which are marked as spam or, even worse, blocked altogether. This decision is based on sender reputation, email content, engagement... --- > You’ve crafted the perfect email campaign, targeted your audience, and hit “send.” But then, an unsettling notification appears in your inbox - Published: 2025-03-21 - Modified: 2025-07-14 - URL: https://www.warmy.io/blog/smtp-error-421-4-7-30-temporary-ban-due-to-abuse-detection-how-to-fix-it/ - Categories: Blog - Tags: Email Deliverability You’ve crafted the perfect email campaign, targeted your audience, and hit “send. ” But then, an unsettling notification appears in your inbox—SMTP Error 421 4. 7. 30. Your emails are temporarily blocked. What now? If you’ve ever experienced bounced emails and delivery failures, you know email deliverability is really important. The dreaded 421 error is the bane of every bulk emailer—the roadblock in front of anyone trying to send bulk emails in the name of marketing, customer outreach or sales follow-ups. If this is only the first time you encounter the error, it might just seem like a minor hiccup. However, it can affect your reputation in the long run if not handled appropriately. In this article, we’ll explain what SMTP Error 421 4. 7. 30 actually is, why you get it, and most importantly how to resolve it. What is SMTP Error 421 4. 7. 30? SMTP Error 421 4. 7. 30 is a temporary error that occurs when an email provider detects potential abuse or spam-like behavior coming from an email sender. The error message appears as: “421 4. 7. 30 – Temporary Ban Due to Abuse Detection”, and this response is given when the sender's account, domain or IP address has been caught in the act of violating policies for sending emails. What this means is that the email provider has put a temporary block for the sender to send an email due to suspected malicious activity or other harmful patterns. Often, this suspension is temporary, and lasts for... --- > SMTP Error 554 5.4.6 "Too Many hops" is one of the most common errors faced by email administrators. - Published: 2025-03-21 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-554-5-4-6-too-many-hops-how-to-fix-it/ - Categories: Blog - Tags: Email Deliverability SMTP Error 554 5. 4. 6 "Too Many hops" is one of the most common errors faced by email administrators. It happens when an email message gets more “hops” than allowed while being passed along between mail servers. To be more specific, this error happens because an email has already "hopped" through several servers. It can then be flagged as problematic and get rejected by the next recipient's email provider. This issue not only disrupts the delivery process, it also delays communications. Ultimately, this results in lower sender reputation that can impact the business in the long run. That is why you should know the steps to take when you see the SMTP Error 554 5. 4. 6 error message, and this guide will assist you in doing so. What is SMTP Error 554 5. 4. 6? SMTP error 554 5. 4. 6 indicates an email has taken too many hops and traveled off course with a distance greater than needed. SMTP means Simple Mail Transfer Protocol, and it is a messaging protocol responsible for sending emails. The “Too Many Hops” error comes from the protocol, which limits how many hops or relays an email can take. So, when an email crosses this threshold, it sets off a “Too Many Hops” error, meaning the message has been routed through too many servers and probably isn’t going to make it to its destination. Q: What are "hops" in email routing? A: In email delivery, a "hop" refers to the journey from mail server... --- > The number of emails sent and received worldwide per day is predicted to reach 408.2 billion by 2027 - Published: 2025-03-21 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-550-5-2-1-mailbox-unavailable-causes-fixes/ - Categories: Blog - Tags: Email Deliverability The number of emails sent and received worldwide per day is predicted to reach 408. 2 billion by 2027. This only shows how important people and businesses perceive email as a communication channel. One of the most common email deliverability problems that email senders and administrators come across is the SMTP Error 550 5. 2. 1. The reason for this error message being sent is when an email cannot be delivered as the recipient mailbox is unavailable. This can be a big issue for those whose businesses or sales are dependent on email to reach others, like marketing efforts. It may be okay for you to tolerate this mistake once, but this will harm your business in the long run the error continues to occur. In this guide, we will help you understand what SMTP Error 550 5. 2. 1 is, how to check mailbox availability, and actionable suggestions to resolve this error. What is SMTP Error 550 5. 2. 1? SMTP stands for Simple Mail Transfer Protocol, which is an industry default standard used to send emails over the internet. When an email message is undelivered, an error message is sent to the sender. This SMTP Error 550 5. 2. 1 points to an issue related to the mailbox of the target receiver. The full error message usually reads something along the lines of “550 5. 2. 1 Mailbox unavailable. ”This is one of the SMTP 550 error codes and commonly indicates that the email sent cannot be delivered and is a permanent failure.... --- > SMTP Error 552 5.2.2 is an error that indicates that the recipient’s mailbox has reached its storage limit. - Published: 2025-03-19 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-552-5-2-2-mailbox-full-how-to-fix-prevent-it/ - Categories: Blog - Tags: Email Deliverability It is a fact: Email communication is one of the most important aspects of daily business and personal interactions. On the other hand, there are times when emails do not reach the recipient, resulting in annoying delivery errors. For example, SMTP Error 552 5. 2. 2 is an error that indicates that the recipient’s mailbox has reached its storage limit. In this guide, we’ll explain why this error happens and how email users and system administrators can fix and even prevent it. These solutions can help you keep an organized inbox to guarantee smooth business email communication. What is SMTP Error 552 5. 2. 2? SMTP Error 552 5. 2. 2 occurs when an email cannot be delivered because the recipient’s mailbox has exceeded its storage limit. When a mailbox fills up, all new incoming emails get rejected with bounced messages with a Mailbox Full error. This problem can have devastating effects to individuals, businesses, and IT administrators—resulting in communication disintegration and delay. This error is frequently seen in email systems with strict quota limits from the email providers such as free accounts or business accounts that have a limited storage. Why does SMTP Error 552 5. 2. 2 happen? In basic terms, SMTP Error 552 5. 2. 2 occurs when an email server rejects an incoming message because of a full mailbox. That being said, there are actually several factors that contribute to this issue—ranging from storage limits imposed by providers to inefficient email management practices. Below are the most common reasons why this... --- > Improve email deliverability in MS365! Learn how to avoid spam filters, boost inbox placement, and maximize engagement. - Published: 2025-03-18 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/outlook-seed-lists-ms365-deliverability-the-battle-between-new-and-established-lists/ - Categories: Blog - Tags: Industry insights Today, ensuring your messages land in the inbox (not the spam folder) is considered a crucial business aspect. Email marketers, sales teams, and businesses rely on high email deliverability to maximize engagement, build trust, and drive conversions. However, reaching the inbox consistently is no easy feat, especially when dealing with complex email filtering systems like Microsoft 365 (MS365). Why seed lists matter in email deliverabilityUsing seed lists is a widely used strategy to gauge and improve email deliverability. These are basically lists consisting of email addresses distributed across different mailbox providers (e. g. , Outlook, Gmail, Yahoo) to help with warming up domains and improving sender reputation before launching large-scale email campaigns. But the question remains—do all seed lists perform equally well? And more importantly, does the type of seed list used impact MS365 deliverability? The role of seed lists in email deliverabilitySeed lists serve a crucial role in improving email performance. See, even if these addresses are not real customers, they can be used to warm up the sender’s domain before engaging in a full on campaign. That way, senders’ domains are already deemed as trustworthy by various ISPs and email providers. When they execute their large-scale outreach campaigns, their emails have a larger chance of landing in the inbox. However, not all seed lists are created equal. But understanding their impact can mean the difference between a successful email campaign and one that fails due to poor inbox placement. The importance of MS365 inbox placement for sendersMicrosoft 365... --- > SMTP Error 554 5.6.0 is one that the email sender never wants to encounter. That means an email was rejected because of content issues. - Published: 2025-03-18 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/smtp-error-554-5-6-0-message-content-rejected-how-to-fix-it/ - Categories: Blog - Tags: Email Deliverability Individuals and businesses rely on email for communication for countless reasons. And so it can be incredibly frustrating when your emails don’t make it to their intended target. For instance, SMTP Error 554 5. 6. 0 is one that the email sender never wants to encounter. That means an email was rejected because of content issues. The recipient’s email server has rejected the message as it violates filtering policies—such as suspected spam-like content, incorrect formatting, or unsupported attachments. For email marketers, this mistake could result in losing email outreach opportunities, decreasing engagement rates, and unnecessary time being spent developing campaigns. IT and email security teams might have trouble figuring out how come their legitimate emails are being rejected, while SaaS email providers need to ensure that their email generated on their platforms always lands in inboxes. What is SMTP Error 554 5. 6. 0? SMTP Error 554 5. 6. 0 is a permanent failure response. It indicates an email has been rejected because of content-related issues. That usually means the recipient’s email server has, upon reviewing the message, determined that it did not meet its filtering criteria and so was blocked prior to delivery. Unlike temporary errors (such as 4. x. x codes), indicates that the message was rejected outright and that it won’t even be retried. This error can be a roadblock because it prevents emails from reaching inboxes, affecting marketing campaigns, customer communication, and business functioning. Common causes of SMTP Error 554 5. 6. 0When an email is rejected due to SMTP Error... --- > SMTP Error 550 5.5.3 means your email provider rejected your email because there were too many recipients. - Published: 2025-03-18 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/smtp-error-550-5-5-3-too-many-recipients-how-to-fix-avoid-it/ - Categories: Blog - Tags: Email Deliverability Have you hit a roadblock with SMTP Error 550 5. 5. 3? You’re not alone. This error is like an invisible barrier between you and the audience, preventing your emails from arriving where they are meant to. And it’s because you’ve exceeded the limit of recipients as defined by the provider of your email service. While bulk emailing is a powerful means of outreach, encountering these restrictions can put a real dent in your workflow (and your campaign’s success). So how do you work within these boundaries without sacrificing your email game? In this guide, we’re going to explain why this error occurs and the best ways to navigate them. However, if you are running outbound sales, marketing campaigns, or an IT infrastructure you will need to be on your toes and adopt these strategies to get emails to your target inboxes. What is SMTP Error 550 5. 5. 3 – Too Many Recipients? SMTP (Simple Mail Transfer Protocol) Error 550 5. 5. 3 means your email provider rejected your email because there were too many recipients. Think of it as an automatic safety mechanism (email service providers put these restrictions in place to reduce spam, prevent server overload and keep email security practices in check). These limits, while maddening, are designed to protect the email system from abuse, both for the sender and for the recipient. These limitations are key to understanding how to properly execute bulk emails and outreach. Let’s explore why this error happens and how different providers enforce sending limits. Common causes... --- > If your emails are suddenly bouncing back with SMTP Error 421 4.7.28, your IP address has been temporarily blocked - Published: 2025-03-18 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/smtp-error-421-4-7-28-ip-temporarily-blocked-causes-how-to-fix-it/ - Categories: Blog - Tags: Email Deliverability If your emails are suddenly bouncing back with SMTP Error 421 4. 7. 28, your IP address has been temporarily blocked by the recipient's email service provider (ESP). No email sender wants this, and all email senders want to solve this. This error typically occurs due to:Spam-like sending behavior (high volume, poor engagement, or suspicious patterns). Failed authentication checks (issues with SPF, DKIM, or DMARC). Reputation issues (your IP has been flagged due to past sending history). If ignored, a temporary block becomes a permanent blacklist, which translates into long-term damage to your sender reputation. In this guide, we’ll explain why this happens and how to find out if your IP is flagged, along with step-by-step solutions to fix it. What is SMTP Error 421 4. 7. 28? SMTP Error 421 4. 7. 28 is a temporary block imposed by an email service provider (ESP) when your sending IP exhibits suspicious or non-compliant behavior. A 4. 7. 28 subcode indicates that the recipient’s email provider has temporarily blocked your IP address, potentially due to security concerns. While your email is not permanently rejected, this error should not be taken lightly. The receiving server has decided to pause acceptance due to potential spam risks or security concerns—and you were most likely identified as one even if you are legitimate. If this error is not addressed and it keeps happening, temporary blocks can escalate to permanent blacklisting. This can significantly impact your ability to send emails in the long run. Common causes of SMTP... --- > Email is a top communication tool, but behind the scenes, strict rules guide its journey to ensure safe delivery across the internet. - Published: 2025-03-13 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/smtp-vs-esmtp-key-differences-and-why-they-matter-for-email-delivery/ - Categories: Blog - Tags: Email Deliverability Email is currently one of the most widely-used forms of communication. These emails need rules to adhere to when they are sent and received to ensure safe passage across the internet. So when you send an email, it actually goes through a rigorous communication process before it can be delivered. Sure, we don’t really see this happening in front of our eyes—but it’s what happens behind the scenes. SMTP (Simple Mail Transfer Protocol) and ESMTP (Extended SMTP) are the two most popular email protocols that determine the way these messages are sent, received, and processed,SMTP has been the standard protocol since the early days of the internet, and ESMTP is essentially an extension or an upgrade that provides added capabilities such as authentication, encryption and improved error handling. For certain businesses, depending on how vital email is to their communications, marketing or transactional needs, understanding how SMTP and ESMTP are different from each other may have lasting effects on the business. This article explains how these protocols work, the reasons why ESMTP is an enhancement over the earlier SMTP, and the advantages of ESMTP implementation to improve the email experience. What is SMTP? It is the standard communication protocol used for sending emails over the Internet. It is in charge of managing the exchange of emails between both mail servers and email clients. SMTP works in a command and response way, wherein the sending server sends a command to the receiving server and waits for the response before issuing the next command.... --- > Authentication failures resulting in blocked or bounced emails are some of the most frustrating problems that senders have to deal with - Published: 2025-03-13 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/smtp-error-451-4-7-23-email-blocked-due-to-spf-failure-how-to-fix-it/ - Categories: Blog - Tags: Email Deliverability Authentication failures resulting in blocked or bounced emails are some of the most frustrating problems that senders have to deal with. And yet, these events are all too common. SMTP Error 451 4. 7. 23 is one of these common mistakes that emerges when an email gets blocked due to not passing the Sender Policy Framework (SPF) check. What is SMTP Error 451 4. 7. 23? SMTP (Simple Mail Transfer Protocol) errors refer to errors encountered in the process of sending mails. SMTP Error 451 4. 7. 23 is an indication that the receiving mail server has temporarily refused the email because it could not verify that the sending server is authorized to send email from the domain. This occurs when the SPF record—one of two important DNS authentication methods—isn’t set up correctly or does not include the mail server sending out the email. SPF failures can even cause real emails to be treated as spam or phishing attempts and thus affect business communications, sales outreach, or customer engagement. Repeated SPF failures, if left unaddressed, can result in an impaired email reputation, lowering the likelihood that your emails will land in inboxes down the line. Why SPF authentication matters for email security and deliverabilitySPF is an email authentication protocol used to prevent and combat email spoofing, a technique that attackers and spammers regularly use to pretend to be mail servers belonging to trusted organizations. When an email is sent, the mail server of the recipient queries whether the sending IP sits behind the sender domain’s... --- > Picture this: You’re about to send out an important email campaign, targeting thousands of potential customers or partners. - Published: 2025-03-13 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-421-4-7-29-suspicious-activity-detected-fixing-email-sending-issues/ - Categories: Blog - Tags: Email Deliverability Picture this: You’re about to send out an important email campaign, targeting thousands of potential customers or partners. You hit “send” with absolute confidence—and are then greeted with a cryptic bounce-back message: “SMTP Error 421 4. 7. 29—Suspicious Activity Detected. ”Panic sets in. What went wrong? Why is your email suddenly being flagged? Even more importantly, how do you resolve it before your email deliverability takes a hit? The error is a red flag to email providers (such as Gmail, Outlook, Yahoo, etc. ) that things are amiss. That could be due to an unanticipated spike in emails, issues with the authentication (SPF, DKIM or DMARC failures or mismatches), or comments of spammy behavior that got credited to your domain. What can start as this temporary measure could go on to cause something worse: long term damage to your domain reputation and ability to enter inboxes in the future. But don’t fret. We’re here for you. In this guide, we’ll explain what SMTP Error 421 4. 7. 29 is, its causes, how to fix it, along with best practices to help prevent it from happening again. What is SMTP Error 421 4. 7. 29? SMTP Error 421 4. 7. 29 is a temporary email rejection due to suspicious actions from your sending domain/IP address. It serves as a protective measure taken by email providers to block spam and prevent phishing and abuse from reaching their users. This error means your emails will not be delivered. Instead, it will defer the emails temporarily. This is... --- > For email senders, one of the most frustrating things that can happen is messages not getting to the intended recipients. - Published: 2025-03-13 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/smtp-error-451-4-5-0-mailbox-unavailable-how-to-fix-it/ - Categories: Blog - Tags: Email Deliverability For email senders, one of the most frustrating things that can happen is messages not getting to the intended recipients. SMTP Error 451 4. 5. 0 – Mailbox Unavailable is one of the common SMTP errors faced by email administration and IT teams. This is a temporary failure so the recipient's mail server rejected delivery but might allow it on another attempt. But if this error is not corrected, emails may continue to bounce or messages would get stuck in the queue. What is SMTP Error 451 4. 5. 0? SMTP (Simple Mail Transfer Protocol) Error 451 4. 5. 0 means that an email server is temporarily rejecting a message because the mailbox is not available. This rejection can happen for a number of reasons, including:The recipient’s mailbox is full, or is temporarily unavailable. The email provider of the recipient is being maintained. DNS misconfigurations or authentication failures. Email rate limits or spam filtering policies blocking the message. Because this is a temporary error, if your email server supports this, it will probably attempt a retry automatically after a while. But when the problem continues, action must be taken to fix email deliverability. Why does this error matter for email deliverability? SMTP errors such as 451 4. 5. 0 can hinder workflow and tarnish sender reputation for businesses and professionals who depend on email for communication. However, when many of your emails receive this error, it may lead to lower email interaction metrics, late communication, higher bounce rates, and blacklisting risks—which are long-term issues. Common causes of... --- > It is easy for Internet Service Providers (ISPs) — such as Gmail, Yahoo, and Outlook to categorize your messages as spam - Published: 2025-03-10 - Modified: 2025-08-07 - URL: https://www.warmy.io/blog/email-engagement-how-seed-list-helps-improve-open-click-rates/ - Categories: Blog - Tags: Email Deliverability It is easy for Internet Service Providers (ISPs) — such as Gmail, Yahoo, and Outlook to categorize your messages as spam or a simple promotional clutter, especially if you have a new or inactive email account. For email marketers, this can be a nightmare. The reason for this ISPs does not have any foundational information about your account, hence, if they noticed that you sent a bulk email with a newly created account, they may consider your account and your email messages spammable. But how can you resolve this? Email engagement holds great significance in establishing sender reputation and securing email deliverability, which is why email warmups in cold outreach are considered as a necessary marketing advantage. Low engagement can negatively impact inbox placement, ultimately reducing conversions and campaign effectiveness, and are one of the reasons why your emails are being routed to spam. One effective way to enhance email engagement and increase open and click-through rates is by leveraging a seed list. In this article, we explain the traditional essence of what an email seed list is and explain how Warmy developed a more innovative approach of taking email seed lists to higher levels for warming up emails, and improving its reputation from different email providers. What is a Seed List? A seed list consists of test email addresses distributed from different email service providers and ISPs. It supplies a controlled testing environment, for an effective analysis of inbox placement, understanding of sender reputation and measurement of engagement performance,... --- > Cold email outreach is a powerful weapon for businesses, but it only works if you can ensure email deliverability - Published: 2025-03-10 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/email-warmup-alternatives-when-traditional-warmup-isnt-enough/ - Categories: Blog - Tags: Email Deliverability Cold email outreach is a powerful weapon for businesses, but it only works if you can ensure email deliverability—that is, the ability to hit the inbox rather than go to spam. Email warmup is one of the most critical steps in achieving high deliverability. It's the practice of gradually increasing the volume of emails sent from your mail server so that email providers build a positive impression of you as a sender. If your business is on a new domain, changing to a new email service provider, or running cold outreach campaigns, then you need to warm up to avoid being flagged as spam. Sending thousands of emails at once from the domains can raise a red flag from ESPs and such emails may get blocked. Hence, traditional warmup methods were introduced—automated interactions where emails are sent and opened create a semblance of organic engagement. While this approach helps, it often falls short due to other factors like spam filters, low engagement rates, inconsistent inbox placements, and domain reputation issues. In a sense, you can say that traditional warmup methods are surface-level only. In this article, we’ll explore Warmy’s email seed list as an alternative, how it compares to traditional warmup, and how to use a seed list as an email warmup alternative. What is traditional email warmup? Traditional email warmup is the process of gradually increasing the volume of emails sent from a new or inactive email account to establish a positive sender reputation with email service providers (ESPs) like... --- > One of the essential factors for any successful email outreach strategy is email deliverability. - Published: 2025-03-07 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/inbox-vs-spam-how-dns-configuration-email-templates-affect-your-email-success/ - Categories: Blog - Tags: Industry insights One of the essential factors for any successful email outreach strategy is email deliverability. It doesn’t matter if you are sending cold emails, marketing campaigns, or transactional messages—they all rely on a few elements to ensure that they actually land in the inbox and not the spam folder. This is where DNS email authentication protocols come into play—SPF, DKIM, and DMARC—these three have a crucial role in proving the legitimacy of your messages. But how much do DNS configurations really impact deliverability? And does even the type of email template you use (plain text vs. HTML) affect your inbox placement? Warmy’s research team set out to answer these questions by conducting a rigorous and data-driven experiment. We analyzed email deliverability data by testing real-world scenarios with different DNS setups and email content formats. Understanding the core DNS records: SPF, DKIM, and DMARCDNS (Domain Name System) records act as the internet’s address book. It is responsible for converting domain names to IP addresses and controlling different domain-related issues and settings. For example: When it comes to email deliverability, the DNS records allow mail servers to verify if an email originated from a trusted sender. A well-configured set of DNS records (SPF, DKIM, and DMARC) minimizes the risk of spoofing, phishing attacks, and spam classification, which means your emails are more likely to land in the inbox. With that said, if you do not specify the right DNS records, even legitimate emails can be delivered in the spam folder. That’s also why SPF,... --- > If you are running email marketing campaigns or doing customer outreach, email deliverability can be a best friend or worst enemy. - Published: 2025-03-07 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-421-4-7-0-temporary-email-rejection-causes-fixes/ - Categories: Blog - Tags: Email Deliverability If you are running email marketing campaigns or doing customer outreach, email deliverability can be a best friend or worst enemy. If you do it correctly, it will return miracles to your business. However, if done incorrectly, can have a very bad effect on your business. As an email sender, there are various issues that you can come across and one of the common errors is SMTP Error 421 4. 7. 0 – Temporary Email Rejection. It's a policy-based, temporary rejection of an email server. Although this rejection is not permanent, multiple rejections can adversely affect sender reputation and ultimately—long-term deliverability of emails. So if your emails are getting temporarily rejected, it’s a sign that something is wrong and you need to address this issue early. What is SMTP Error 421 4. 7. 0? SMTP Error 421 4. 7. 0 is a temporary email rejecting error. Unlike a hard bounce, when an email cannot be delivered permanently (for instance, because the address being sent to is invalid), this error means that the recipient’s mail server has temporarily blocked the delivery of the message, but may allow safe passage to go through later. How SMTP Error 421 4. 7. 0 affects email deliverabilitySMTP Error 421 4. 7. 0 is a temporary rejection that can have a long-term impact on your email deliverability and sender reputation. Let’s explore how this error affects your email performance — and what it means for your overall deliverability strategy. Temporary rejections can lead to permanent blocksIf an email... --- > A decline in the sender’s IP or domain reputation is most likely the reason why their emails are going to junk or spam - Published: 2025-03-07 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/google-postmaster-issues-fixing-bad-ip-domain-reputation/ - Categories: Blog - Tags: Email Deliverability A decline in the sender’s IP or domain reputation is most likely the reason why their emails are going to junk or spam, which can result in an equal decline in open rates. There are, of course, a number of practical strategies to improve your open rates. The use of Google Postmaster tools offers valuable insights into your sender's reputation. This advantage is required by many email users to ensure high email deliverability. However, many email marketers struggle to interpret and act on this data effectively. Leveraging seed list testing is a powerful strategy for diagnosing and fixing deliverability issues. It uses a controlled test environment, allowing businesses to pinpoint any deliverability problems before they escalate into something they cannot resolve. In this article, we will explore how to diagnose and resolve bad IP and domain reputation issues using Google Postmaster Tools, with a specific focus on how seed list testing can help businesses monitor and improve email deliverability. Understanding Google Postmaster ToolsGoogle Postmaster Tools is a free platform that provides email senders with valuable analytics related to their email performance on Gmail. These insights help businesses understand whether their emails are being delivered successfully or flagged as spam. Useful Metrics in Google Postmaster ToolsIP Reputation – Provides measurements on how Gmail perceives the sender’s IP address. If you have a lower inbox placement that means that you potentially have a poor IP reputation. Domain Reputation – Assess the trustworthiness of the sender’s domain. A bad domain reputation increases the... --- > Crazy to think what happens when you hit "Send"—your email races through networks, security checks & spam filters in seconds! - Published: 2025-03-05 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/spf-alignment-issues-causes-fixes-best-practices-for-better-email-authentication/ - Categories: Blog - Tags: Email Deliverability It’s mind-blowing sometimes to think about everything that goes on behind the scenes when you click on “Send” after writing an email. In seconds, your message goes on a complex journey—getting relayed over networks, through authentication checkpoints, and under multiple security layers before it arrives in your recipient’s inbox (or, if luck’s not in your favor, their spam folder). SPF (Sender Policy Framework) is an important authentication protocol used to make sure that your email arrives safely. Designed to prevent spoofing and phishing, SPF enables mail servers to check whether an email originated from an authorized source. But SPF alone is not immutable and it must be properly aligned with the sender’s domain in order to truly work. SPF record configuration issues, alignment mismatch issues, third-party sending services, and other issues can cause rejection, spam filtering, and deliverability nightmares. This is why SPF alignment issues should matter to IT administrators, email security experts, and marketers who use email in their business growth and communication. What is SPF alignment? SPF alignment means that the domain used in the Return-Path (also called the "envelope-from" or "MailFrom" domain) matches the domain in the From address that the recipient sees in their inbox. If these domains are the same or share the same root domain (depending on the alignment mode), SPF alignment passes. If they are different, SPF alignment fails, which can affect DMARC authentication and potentially result in emails being rejected or marked as spam. How SPF alignment worksWhen an email is sent, the... --- > Error 421 is likely the cause of heavy load or maintenance from the server’s side, variant 4.4.3 means that there may be some misconfiguration - Published: 2025-03-05 - Modified: 2025-08-07 - URL: https://www.warmy.io/blog/smtp-error-421-4-4-3-routing-server-failure-causes-solutions/ - Categories: Blog - Tags: Email Deliverability You may often see the error:SMTP transient error: 421 Service Not Available And think that you can just wait it out. This can be true for some of the SMTP email error 421, but its variants may have severe repercussions on your email deliverability. One of its variants that may require immediate attention is the SMTP Error 421 4. 4. 3 – Routing Server Failure. Although email servers may not reject your emails straightaway, it can still result in SMTP deferrals, and too many retries can harm the email. Although this error may pertain to a temporary issue due to heavy load or maintenance, frequent occurrences of this can mean that something more problematic is at hand — such as incorrect email settings, or issues with IP address reputation (blacklist). And just like other SMTP errors and codes, this should be taken seriously. While conducting some email deliverability tests from Warmy and proper configuration of email authentication settings can do the trick, understanding the varying factors why it happened can also help as a preventive strategy. Varying Causes of SMTP error 421 4. 4. 3? SMTP error 421 4. 4. 3 can develop due to a number of technical issues. It can range from server configuration issues to much broader network disruptions. This issue pertains to an error in the email server, which results in the inability of the mail server to correctly direct messages to the intended recipient. It can either be the result of: Misconfiguration of the mail... --- > Sending limits and anti-spam measures are being imposed by Internet Service Providers (ISPs) and Email Service Providers - Published: 2025-03-05 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-421-4-7-26-email-rate-limit-exceeded-causes-fixes/ - Categories: Blog - Tags: Email Deliverability Ensuring that your emails land in recipients’ inboxes is getting more and more complex. Sending limits and anti-spam measures are being imposed by Internet Service Providers (ISPs) and Email Service Providers (ESPs) to prevent unwanted emails from reaching users. As a result, errors sometimes occur for even legitimate senders—affecting their email campaigns. The SMTP Error 421 4. 7. 26, for instance, is a widely supported code from many email servers when a rate limit has been reached and messages are temporarily rejected. This happens most commonly when the sender sends many emails to many recipients in a short period of time, which in turn activates throttling mechanisms designed to prevent spam. Nevertheless, if not managed properly, it can have a massive impact on email deliverability, campaign performance, and sender reputation. What is SMTP Error 421 4. 7. 26 and what does it mean? SMTP Error 421 4. 7. 26. indicates that the recipient’s email server has temporarily refused messages because the sender has hit sending rate limits. So actually SMTP 421 is a temporary error code, which indicates the server has rejected the message but the sender can try later. Whereas permanent errors (5xx errors) indicate that the email cannot be delivered, 421 errors do not—they just mean that the server cannot take a message at this moment or that it is applying restrictions. A typical 421 error message may look like this:CopyEdit421 4. 7. 26 – Email rate limit exceeded, try again later. Each part of the code has a specific meaning:"421": Indicates... --- > eing exposed to email security risks is something we all want to avoid; security risks such as man-in-the-middle (MITM) attacks - Published: 2025-03-05 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-starttls-errors-causes-fixes-how-to-ensure-secure-email-communication/ - Categories: Blog - Tags: Email Deliverability Being exposed to email security risks is something we all want to avoid; security risks such as man-in-the-middle (MITM) attacks, where attackers intercept and manipulate email traffic, are the bane of all email marketer’s existence. There are the basics of ensuring a configured DNS and SMTP setting, but some errors go deeper than that. Some email users receive errors such as:Authentication failure An error that stemmed from when an email client or server fails to establish a secure TLS connection — a security protocol that preserves privacy and data security. Conducting an email deliverability test is a contributing factor allowing email users to perform proper evaluation and avoid some common and complex errors that are affecting their email deliverability. However, we at Warmy. io understand that it would take a lot more to avoid such errors, which is why we’ve developed a variety of tools to improve the overall email process. But first, let us understand what STARTTL is, and what are its repercussions that affect your overall email experience? What is STARTTLS? STARTTLS is used to upgrade a plain-text email connection to a secure, encrypted connection using TLS (Transport Layer Security). It is a protocol common that helps boost email security by preventing unauthorized access to transmitted messages. STARTTLS works by:Connecting an email client to an SMTP server via an unencrypted connection. The client issues the STARTTLS command, requesting encryption. If the server supports TLS, it upgrades the connection to a secure one. Emails are transmitted securely, preventing data... --- > Email deliverability is essential to any effective email marketing or transactional email plan. Receiving SMTP Error 451 4.7.26 - Published: 2025-03-05 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-451-4-7-26-email-blocked-due-to-poor-domain-reputation/ - Categories: Blog - Tags: Email Deliverability Email deliverability is essential to any effective email marketing or transactional email plan. Receiving SMTP Error 451 4. 7. 26 can be annoying and damaging to your communication endeavors. However, this comes with a caveat because this error indicates that your emails are being rejected due to poor domain reputation. This, in turn, leads to temporary blocks and poor deliverability. In this guide, we’ll take a look at what causes this SMTP error, how domain reputation affects your email deliverability, and the actions you should take to troubleshoot and recover from it. What is SMTP Email Error 451 4. 7. 26? SMTP Error 451 4. 7. 26 is an email server temporary rejection due to bad domain reputation. This usually means that the recipient’s mail server has flagged your domain as suspicious, untrustworthy, or likely to send spam. There are several reasons for it, and knowing those can help you identify the problem and resolve it. It’s similar to your email being your passport and the receiving email provider being the Immigration Control. They consider you shady or questionable—and stop you from crossing. To resolve the issue, you need to establish trust to make your domain reputable. This is a common problem with all large mail service providers, such as Gmail, Yahoo, and Outlook, which have advanced filters that decide whether an email gets delivered to inboxes, sent to spam, or rejected entirely. If you’re composing an email and you receive an error message similar to the one pictured below, your domain reputation may... --- > Now more than ever, email security is vital. Cybercriminals leverage email vulnerabilities to impersonate businesses - Published: 2025-03-05 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-451-4-7-24-dmarc-policy-failure-causes-solutions/ - Categories: Blog - Tags: Email Deliverability Imagine this; you have already put in hours working on the perfect email campaign, you personalized every message, you took the time to double-check everything, there are no typos and you hit “send” only to find out your emails are getting blocked. No warning, no real explanation—just an obscure bounce message: “SMTP Error 451 4. 7. 24 – DMARC Policy Failure. ”If this is starting to sound familiar, you’re not alone. A lot of businesses and email marketers struggle with this annoying error without being able to fully comprehend why their emails are not accepted. In this article, we’ll explain what SMTP 451 4. 7. 24 means, why DMARC failures cause email rejection, as well as how to resolve them so your emails find their way into inboxes instead of spam folders. What is SMTP Error 451? SMTP (Simple Mail Transfer Protocol) is a set of rules that servers follow to send and receive messages. But when things go wrong—especially with security authentication—your email server may respond with an SMTP 451 error indicating a temporary rejection. The 4. 7. 24 error code is a special case that indicates a DMARC (Domain-based Message Authentication, Reporting, and Conformance) policy failure, which means your email failed an authentication check. What is DMARC and why is it important? Now more than ever, email security is vital. Cybercriminals leverage email vulnerabilities to impersonate businesses, send phishing emails and commit fraud daily. This is where DMARC steps in. It isn’t just another email security protocol. It’s a policy layer that ensures... --- > One of the many reasons why your emails are probably going to spam or junk is because you have a new email or domain - Published: 2025-03-04 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/the-science-and-process-of-warming-up-newly-created-email-domains/ - Categories: Blog - Tags: Industry insights Crafting effective marketing email content is just one of the fundamentals that can make an effective email outreach successful. In the realms of email marketing the technical aspects are just as crucial as the marketing ploy; our research team devoted their time to understanding the best and most helpful technical factors that can help every email user and marketer with the ability to achieve the best email deliverability and reputation. For this research, our team examined how different warm-up strategies affect the deliverability of emails from newly created domains. We’ve tested various flows, each focusing on different approaches that includes:Gradual and moderate volume increasesPassive engagementContent diversificationMailbox redirect assessment Delayed sendingPlatform-specific warm-ups,Platform diversity testingOur objective is to determine the best practice for optimizing domain reputation and ensure high deliverability rates. A Deeper Look Into Our Research’s Objectives One of the many reasons why your emails are probably going to spam or junk is because you have a new email or domain. Many Internet Service Providers (ISPs) may have an issue with new or inactive email addresses when it comes to sending bulk, or large quantities of emails. ISPs do not have any established data for new domains and inactive mailboxes, so when these new or inactive emails send a large number of messages there is a large chance that it may direct their message to spam. Email warmup is, therefore, crucial in establishing a trustworthy sender reputation before large-scale outreach. What We Did and How We Did ItOur research team conducted... --- > The most difficult part of creating email content and developing email marketing strategies is actually crafting the campaign right? - Published: 2025-03-04 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/fixing-smtp-error-421-4-4-2-bad-connection-what-you-need-to-know/ - Categories: Blog - Tags: Email Deliverability The most difficult part of creating email content and developing email marketing strategies is actually crafting the campaign right? Not really. If you are an email marketer or have done some campaigns, you understand that there is more to email marketing than simply creating content, strategizing campaigns, and then hitting send. You need to employ tons of proactive measures to avoid any email issues, and errors that might damage not only the entire campaign you’ve constructed — but also the email reputation that you’ve protected. One of the SMTP errors that achieved notoriety due to its capability to potentially create significant disruptions is SMTP Error 421 4. 4. 2. An SMTP error can lead to failure or delayed messages due to your email server being incapable of establishing a stable connection with the recipient’s mail server. Having any delayed messages can of course lead to issues with your email deliverability. And here at Warmy. io, we’ve developed the best systems — such as the free email deliverability test to help you achieve a reputable email account. We can guarantee that receiving the SMTP error 421 4. 4. 2 Bad Connection, is not only solvable but is also avoidable. Let’s uncover more about this error, and how Warmy can supply the best solution for this issue. What Causes SMTP Error 421 4. 4. 2? This error typically results from server, network, or sender-side issues. Let’s explore them in detail. Server-Side IssuesThe recipient’s mail server is temporarily down or overloaded. Misconfigurations in... --- > Server congestion, or SMTP error 421 4.4.5, happens when an email server is overloaded with incoming or outgoing email requests. - Published: 2025-03-04 - Modified: 2025-07-14 - URL: https://www.warmy.io/blog/how-to-solve-smtp-error-421-4-4-5-server-congestion-issues/ - Categories: Blog - Tags: Email Deliverability Email is key for both personal and professional lives. But when an email doesn’t make it to its recipient, it can cripple the business, lead to missed opportunities, and ultimately loss of revenue. Server congestion, or SMTP error 421 4. 4. 5, happens when an email server is overloaded with incoming or outgoing email requests. This might cause lagging in processing the messages or even a total failure of the delivery. This can be damaging to email marketing campaigns, transactional emails, and business communications of businesses and IT teams overall. In this guide, we’ll discuss what triggers SMTP 421 4. 4. 5, how to resolve it, and what steps you can take to avoid it in the future. What is the reason SMTP Email Error 421 4. 4. 5? What causes SMTP Email Error 421 4. 4. 5? The SMTP Error 421 4. 4. 5 message typically indicates that the email server is busy or has other issues like network failures, too many users sending emails to the server, etc. Below we discuss these contributing factors in detail. Server-side factorsHigh email traffic: An email server may get overwhelmed when there are too many outgoing or incoming email requests than it can handle. Bulk email campaigns, marketing blasts, or automated transactional emails might bombard the server. Congestion can occur due to sudden bursts of email volume (for example, announcements or newsletters). Not enough CPU, memory, or bandwidth: If the mail server has insufficient resources (e. g. , CPU, RAM, storage, or bandwidth), the server cannot process emails... --- > One of the top channels of communication for businesses is email, which unfortunately makes it one of the prime targets of cyberthreats like phishing - Published: 2025-02-28 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-connection-encryption-the-key-to-secure-reliable-email-delivery/ - Categories: Blog - Tags: Email Deliverability One of the top channels of communication for businesses is email, which unfortunately makes it one of the prime targets of cyberthreats like phishing, data interception, and spoofing. Encryption is the answer. Without it, emails are transmitted as plaintext over the Internet where people can steal sensitive information. SMTP (Simple Mail Transfer Protocol) is the standard protocol for sending emails, but it is not secure by default. To protect email communications, SMTP encryption is essential. In this blog, you will learn how SMTP encryption works, the difference between TLS and SSL, and best practices to help you achieve email security. What is SMTP and why it needs encryptionSMTP is the protocol that does the heavy lifting when it comes to routing an email from the sender’s email server to the intended recipient’s inbox. But SMTP only makes sure that emails get delivered, it does not offer security by default. SMTP is based on the client-server model, where the sending mail server is the client, and the receiving mail server is the server. It uses commands and responses, like HELO, MAIL FROM, and RCPT TO. There is no default encryption built into Simple Mail Transfer Protocol (SMTP), meaning that attackers are able to intercept, alter and spoof SMTP messages. To secure this process, encryption mechanisms are being used such as TLS (Transport Layer Security) and SSL (Secure Sockets Layer). SMTP sends emails in plaintext by default, which is its biggest disadvantage, as it is prone to many security threats, such as: Man-in-the-Middle (MITM) Attacks: Cybercriminals can... --- > One of these temporary errors is the SMTP error 421 4.3.2 (Service Shutting Down), an incident where a mail server unexpectedly closes down. - Published: 2025-02-28 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-error-421-4-3-2-service-shutting-down-causes-how-to-fix-it/ - Categories: Blog - Tags: Email Deliverability There are tons of SMTP related errors that an average email user can encounter. Some of them can be due to IP reputation concerns, while others are rooted and are likely the result of a temporary errors failure — retryable errors. One of these temporary errors is the SMTP error 421 4. 3. 2 (Service Shutting Down), an incident where a mail server unexpectedly closes down. Encountering this, of course, will result in email delivery interruptions, but it is highly unlikely that the issue is caused on your end. This issue can stem from server overload or scheduled maintenance. However, there are some instances in which this error occurs due to a misconfigured setting that prevents emails from being processed. Understanding the cause of this error is the first step. Although you are receiving this error from a server overload, you cannot neglect other factors that may affect your email deliverability. In this guide, we’ll explain what SMTP error code 4. 3. 2 is, its impact on email servers, how to fix it, and what are some of the best practices to prevent future occurrences. What Causes This Issue? SMTP error 421 4. 3. 2 – Service Shutting Down typically indicates a temporary failure on the mail server. This means that the error is a result of uncontrollable factors such as mail server overloads, or scheduled maintenance. However, you can still receive this error message if there are some sending limitations implemented in your account, or your email is blacklisted.... --- > Having Warmy as your overall email deliverability system can provide you with the capability to configure your SMTP setting - Published: 2025-02-28 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/how-smtp-auth-mechanisms-affect-email-deliverability-and-security/ - Categories: Blog - Tags: Email Deliverability SMTP Authentication (SMTP AUTH) is not only a fundamental mechanism that protects your emails against spoofing and phishing attacks. It also has a direct contribution to your email deliverability and brand recognition. Depending on how well you set up your SMTP AUTH you are less likely to experience SMTP errors related to authentication failures —potentially SMTP Email Error 500 5. 7. 1—, email bounces, and poor inbox placements. However, proper SMTP configuration is easier said than done. Having Warmy as your overall email deliverability system can provide you with the capability to configure your SMTP setting, besides on its well-known features, such as its free email deliverability test. For this blog, we will take a deep examination of SMTP AUTH and what exactly is its contribution to email deliverability and the improvement of email security? Explaining the Essence of SMTP AUTHBefore sending messages, email clients need to undergo an authentication process with the mail server, to ensure that only the authorized users can send emails from specific domains. This extended protocol is known as SMTP AUTH and its process involves the following steps:The email client initiates an SMTP session with the mail server. The client provides authentication credentials or a token. The server verifies the credentials and grants access. The email is sent securely if authentication is successful, preventing unauthorized senders from using the mail server. It prevents unauthorized access, that prevents email spoofing, secure your email account against unauthorized access, and ensure that your reputation is protected. It also... --- > SMTP AUTH mechanisms explained: Learn how to choose the right authentication method for secure and reliable email sending. - Published: 2025-02-26 - Modified: 2025-04-09 - URL: https://www.warmy.io/blog/smtp-auth-mechanisms-explained-choosing-the-right-authentication-for-secure-email-sending/ - Categories: Blog - Tags: Marketing Phishing attacks, and spam emails remain a continuous problem for many email users. One of the most notorious forms of email security issue is the unauthorized access or usage of a bad actor or a spammer towards an email. If this ever happened to you then that means that you probably have an issue with your SMTP authentication (SMTP AUTH). SMTP Authentication is an important mechanism guaranteeing that the only authorized users can send emails through the mail servers, prevents unauthorized use and maximizes email deliverability. Improving your overall email deliverability is the lifeblood of our workforce here at Warmy, our services is not limited to our free email deliverability test, our users can also take advantage of our free SPF Record Generator that can help specify which mail servers have the authority to send emails for a specific domain. But first, let us try to take a deeper look at SMTP authentication, how it actually works and what are its importance for email security. You Can Also Read Our Support Page on How To Configure SMTP with Warmy. Understanding SMTP Authentication: How It Works and Its ImportanceSMTP (Simple Mail Transfer Protocol) is used for email transmission, therefore making it a standard communication protocol. Here is how it goes. Upon sending an email, the SMTP client communicates with the SMTP server then forwards the message to the recipient’s mail server. Without any form of authentication, malicious actors could exploit SMTP servers to send spam emails. Thus, making SMTP authentication a... --- > Email is an instrumental communication tool that finds its advantages in areas such as marketing, customer support. - Published: 2025-02-26 - Modified: 2025-08-11 - URL: https://www.warmy.io/blog/fixing-reverse-dns-lookup-failures-best-practices-for-email-server-configuration/ - Categories: Blog - Tags: Marketing Email is an instrumental communication tool that finds its advantages in areas such as marketing, customer support, and other internal communication processes. Email marketing is considered as the “king of all marketing channels”, while email communication for both customer support and internal communication offers a non-time sensitive system allowing everyone without rushing too much of the information. Here at Warmy. io, we understand the immense value of emails for almost everyone in the professional landscape; giving us the opportunity to implement an All-In-One tool for email deliverability. With our boundless offerings of free tools such as our free email deliverability test. However, we also understand that there are a variety of factors that may affect your email deliverability. When an email user consistently gets their emails marked as spam, gets rejected by mail servers, or when you understand that your email reputation is suddenly depleting then it is most likely the cause of a Reverse DNS (rDNS) lookup failure. Reverse DNS helps email servers verify that the sending server’s IP address resolves to a legitimate domain. When this verification fails, mail servers may reject emails, flag them as spam, or lower your sender reputation, impacting your ability to reach inboxes. Explaining Reverse DNS Lookup and its ImportancerDNS lookup is a procedure that involves mapping an IP address back to its associated domain name. It is a verification process utilized by mail servers to guarantee that the genesis of the email is legitimate and from a trusted source. Simply put, it... --- ---