{"id":4031,"date":"2025-03-13T11:00:12","date_gmt":"2025-03-13T11:00:12","guid":{"rendered":"https:\/\/www.warmy.io\/blog\/smtp-error-451-4-7-23-email-blocked-due-to-spf-failure-how-to-fix-it\/"},"modified":"2026-04-05T13:02:16","modified_gmt":"2026-04-05T13:02:16","slug":"smtp-error-451-4-7-23-email-blocked-due-to-spf-failure-how-to-fix-it","status":"publish","type":"post","link":"https:\/\/www.warmy.io\/blog\/smtp-error-451-4-7-23-email-blocked-due-to-spf-failure-how-to-fix-it\/","title":{"rendered":"SMTP Error 451 4.7.23: Email Blocked Due to SPF Check Failure \u2014 Causes and Fixes"},"content":{"rendered":"<p><span>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 <\/span><a href=\"https:\/\/www.youtube.com\/watch?v=O9kAtrR-DIQ\" rel=\"noopener\" target=\"_blank\" rel=\"noopener noreferrer\"><span>Sender Policy Framework (SPF)<\/span><\/a><span> check.<\/span><\/p>\n<h2><b>What is SMTP Error 451 4.7.23?<\/b><\/h2>\n<p><span>SMTP (<\/span><a href=\"https:\/\/www.warmy.io\/blog\/what-is-smtp-and-how-does-the-smtp-server-work\/\" target=\"_blank\" rel=\"noopener noreferrer\"><span>Simple Mail Transfer Protocol<\/span><\/a><span>) 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\u2002temporarily refused the email because it could not verify that the sending server is authorized to send email from the domain.<\/span><\/p>\n<p><span>This occurs when the SPF record\u2014one of two important DNS authentication methods\u2014isn\u2019t set up correctly or does not include\u2002the mail server sending out the email.<\/span><\/p>\n<p><span>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\u2002failures, if left unaddressed, can result in an impaired email reputation, lowering the likelihood that your emails will land in inboxes down the line.<\/span><\/p>\n<h3>Why SPF authentication matters for email security and deliverability<\/h3>\n<p><span>SPF is an<\/span><a href=\"https:\/\/www.warmy.io\/blog\/how-smtp-auth-mechanisms-affect-email-deliverability-and-security\/\" target=\"_blank\" rel=\"noopener noreferrer\"> <span>email authentication protocol<\/span><\/a> <span>used to prevent and combat email spoofing, a technique that attackers and spammers regularly use to pretend to be mail servers belonging to trusted\u2002organizations. When an email is sent, the mail server of the recipient queries whether the sending IP sits behind\u2002the sender domain\u2019s SPF record If the check fails, the email may be:<\/span><\/p>\n<ul>\n<li><span>Rejected (SMTP Error 451 4.7.23)<\/span><\/li>\n<li><span>Marked as spam<\/span><\/li>\n<li><span>Quarantined or delayed<\/span><\/li>\n<\/ul>\n<p><span>SPF authentication plays a crucial role in:<\/span><\/p>\n<ul>\n<li><span>Enhancing email security by protecting against domain spoofing and phishing attacks<\/span><\/li>\n<li><span>Improving email deliverability by identifying legitimate senders<\/span><\/li>\n<li><span>Maintaining good sender reputation with email service providers (ESPs)<\/span><\/li>\n<\/ul>\n<p><span>However, SPF failures can happen due to misconfigured DNS records, too many SPF lookups, email forwarding, or unauthorized third-party senders. Knowing the causes and finding the correct solution is the key to fixing\u2002email deliverability.<\/span><\/p>\n<h2><b>Common causes of SPF failures leading to Error 451 4.7.23<\/b><\/h2>\n<p><span>If your email server fails SPF authentication, the recipient\u2019s mail server may return SMTP Error 451 4.7.23, temporarily rejecting the email due to SPF policy violations. Below are the most common causes of SPF failures and how they lead to this error.<\/span><\/p>\n<h3>Missing or misconfigured SPF record<\/h3>\n<p><span>If a domain does not have an SPF record, recipient mail servers have no way of verifying whether the sending server is authorized. A misconfigured SPF record can also lead to failures if:<\/span><\/p>\n<ul>\n<li><span>The SPF record contains syntax errors<\/span><\/li>\n<li><span>The record does not include all necessary email servers<\/span><\/li>\n<li><span>Multiple SPF records exist (SPF only supports one record per domain)<\/span><\/li>\n<\/ul>\n<p><b>Example of a correct SPF record format: <\/b><span>A correctly formatted SPF record should follow a structured syntax. Below is an example of a standard SPF record:<\/span><\/p>\n<p><span>v=spf1 ip4:192.168.1.1 include:_spf.google.com -all\u00a0\u00a0<\/span><\/p>\n<h3>Exceeding SPF DNS lookup limit<\/h3>\n<p><span>SPF records cannot exceed 10 DNS lookups. This is a strict limit set to prevent SPF validation from causing excessive DNS queries, which could slow down email processing. Every <\/span><span>include<\/span><span>, <\/span><span>a<\/span><span>, <\/span><span>mx<\/span><span>, and <\/span><span>ptr<\/span><span> mechanism in an SPF record counts as a lookup. If you exceed 10 lookups, the recipient\u2019s mail server will automatically fail SPF validation, even if the record is correct.<\/span><\/p>\n<h3>Email forwarding and SPF failures<\/h3>\n<p><span>SPF relies on checking the original sending IP address. However, when an email is forwarded, the return path changes, and the forwarder\u2019s server becomes the \u201cnew sender.\u201d Since the forwarder\u2019s IP is not included in the original SPF record, SPF fails, leading to SMTP Error 451 4.7.23.<\/span><\/p>\n<p><span>When an email is forwarded, SPF validation often fails because:<\/span><\/p>\n<ul>\n<li><span>The recipient\u2019s mail server checks the forwarder\u2019s IP instead of the original sender<\/span><\/li>\n<li><span>The forwarder is not authorized in the SPF record<\/span><\/li>\n<li><span>If DMARC (Domain-based Message Authentication, Reporting &amp; Conformance) is strict, SPF failures lead to email rejection<\/span><\/li>\n<\/ul>\n<h3>4. Unauthorized third-party email senders<\/h3>\n<p><span>Most businesses are using third-party services to send emails like email marketing tools, CRM systems, automation\u2002tools, etc. It means if these services are not on your SPF record, all the emails sent by them will fail SPF checks and may actually get\u2002blocked.<\/span><\/p>\n<h3>5. Conflict with other authentication protocols (DKIM &amp; DMARC)<\/h3>\n<p><span>SPF is just one part of email authentication. It works best when combined with:<\/span><\/p>\n<ul>\n<li><b>DKIM (DomainKeys Identified Mail):<\/b><span> Provides emails with a cryptographic signature that authenticates the\u2002emails<\/span><\/li>\n<li><b>DMARC (Domain-based Message Authentication, Reporting &amp; Conformance):<\/b><span> Specifies how SPF and DKIM failures should be processed. Now, if DMARC is <\/span><span>p=reject<\/span><span> and still failing, the email gets dropped.<\/span><\/li>\n<\/ul>\n<p><b>\ud83d\udd16 Related Reading:<\/b><a href=\"https:\/\/www.warmy.io\/blog\/why-do-you-need-to-configure-spf-dkim-and-dmarc\/\" target=\"_blank\" rel=\"noopener noreferrer\"> <span>SPF, DKIM, and DMARC: Boosting Email Security and Deliverability<\/span><\/a><\/p>\n<h2><b>How to fix SMTP Error 451 4.7.23 and SPF failures<\/b><\/h2>\n<p><span>There is nothing beneficial or advantageous about SMTP errors. So if\u2002you get this error code, it\u2019s not the end of the world\u2014and there are things you can do to work around it.\u00a0<\/span><\/p>\n<h3>Step 1: Verify your SPF record<\/h3>\n<p><span>Before editing anything, you must\u2002first verify that you have an existing SPF record in place and also to see if it is configured properly. Use the nslookup\u2002command in the terminal to check your SPF record:<\/span><\/p>\n<p><b>Windows\/macOS\/Linux:<\/b><\/p>\n<p><span>nslookup -type=TXT yourdomain.com<\/span><\/p>\n<p><span>This will return the SPF record (if one exists) associated with your domain.<\/span><\/p>\n<p><span>Example output:<\/span><\/p>\n<p><span>yourdomain.com text = \u201cv=spf1 ip4:203.0.113.5 include:_spf.google.com -all\u201d<\/span><\/p>\n<p><span>If no SPF record is found or it is incorrect, you need to create or update it in your DNS settings. Alternatively, you can use online SPF validation tools such as<\/span><a href=\"https:\/\/www.warmy.io\/free-tools\/spf-generator\" target=\"_blank\" rel=\"noopener noreferrer\"> <span>Warmy\u2019s Free SPF Record Generator<\/span><\/a><span>.<\/span><\/p>\n<h3>Step 2: Reduce DNS lookups in SPF<\/h3>\n<p><span>Since SPF allows only 10 DNS lookups, exceeding this limit causes SPF failures. If your SPF record contains too many <\/span><span>include<\/span><span> mechanisms, you need to reduce the number of lookups through<\/span><a href=\"https:\/\/www.warmy.io\/blog\/what-is-spf-flattening-and-how-it-can-simplify-your-spf-records-without-losing-functionality\/\" target=\"_blank\" rel=\"noopener noreferrer\"> <span>SPF flattening<\/span><\/a><b>.\u00a0<\/b><\/p>\n<h3>Step 3: Address forwarding-related SPF failures<\/h3>\n<p><span>SPF fails when emails are forwarded because the recipient\u2019s server sees the forwarder\u2019s IP instead of the original sender\u2019s IP. To fix this issue:<\/span><\/p>\n<ul>\n<li><b>Implement DKIM (DomainKeys Identified Mail). <\/b><span>DKIM signs outgoing emails so they remain valid even if forwarded. Ensure your email provider supports DKIM signing.<\/span><\/li>\n<li><b>Use DMARC to allow SPF failures for forwarded emails. <\/b><span>DMARC allows you to specify \u201crelaxed\u201d policies that do not reject forwarded emails.<\/span><\/li>\n<li><b>Enable ARC (Authenticated Received Chain). <\/b><span>Some email providers support ARC headers, which help preserve SPF authentication across email forwards.<\/span><\/li>\n<\/ul>\n<p><span>If SPF failures persist after forwarding, whitelisting trusted forwarders on the recipient side may help.<\/span><\/p>\n<h3>Step 4: Authorize third-party email services<\/h3>\n<p><span>If you use email marketing tools, CRM platforms, or transactional email services, you must explicitly authorize them in your SPF record. To identify third-party services sending emails on your behalf:<\/span><\/p>\n<ol>\n<li><span>Check email headers for unknown mail servers.<\/span><\/li>\n<li><span>Review your email provider\u2019s documentation for SPF recommendations.<\/span><\/li>\n<li><span>Use DMARC reports to detect unauthorized senders.<\/span><\/li>\n<\/ol>\n<p><span>Then, you can find the correct SPF <\/span><span>include<\/span><span> value for the service and add it to your SPF record.<\/span><\/p>\n<h3>Step 5: Align SPF with DKIM and DMARC for stronger authentication<\/h3>\n<p><span>SPF alone is not enough to fully protect email deliverability. It works best when combined with DKIM and DMARC.<\/span><\/p>\n<h4><b>Why DMARC helps enforce email authentication<\/b><\/h4>\n<p><span>DMARC ensures emails failing SPF or DKIM are handled properly. It also provides reporting to help detect unauthorized senders.<\/span><\/p>\n<h4><b>How to set up a DMARC policy that prevents false positives<\/b><\/h4>\n<ol>\n<li><span>Start with a relaxed DMARC policy. This monitors failures without blocking emails.<\/span><\/li>\n<li><span>Gradually enforce DMARC:<\/span> <span>v=DMARC1; p=quarantine; pct=50; rua=mailto:reports@yourdomain.com;<\/span>\n<ul>\n<li><span>p=quarantine<\/span><span> moves 50% of failed emails to spam.<\/span><\/li>\n<li><span>rua<\/span><span> sends reports of failed emails to your inbox.<\/span><\/li>\n<\/ul>\n<\/li>\n<li><span>Fully enforce DMARC once everything is correct. This blocks all unauthorized emails.<\/span><\/li>\n<\/ol>\n<h2><b>Best practices to prevent future SPF errors<\/b><\/h2>\n<h3>Regularly monitor SPF records and DNS changes<\/h3>\n<p><span>SPF records are stored in the Domain Name System (DNS), and any changes to your email service providers, mail server IPs, or domain configuration can affect SPF validation.\u00a0<\/span><\/p>\n<p><b>Why SPF records should be monitored regularly:<\/b><\/p>\n<ul>\n<li><span>Many email services (Google Workspace, Microsoft 365, Mailchimp, SendGrid, etc.) change their SPF policies or IP addresses periodically. You must stay updated and adjust your SPF record accordingly.<\/span><\/li>\n<li><span>If your organization starts using a new CRM, email marketing platform, or transactional email service, you must update SPF records to reflect the new senders.<\/span><\/li>\n<li><span>If your domain provider updates DNS settings or a DNS admin accidentally modifies SPF records, email authentication failures can occur.<\/span><\/li>\n<\/ul>\n<p><b>Now, here\u2019s how you can monitor your SPF records effectively:<\/b><\/p>\n<ul>\n<li><span>Set up automated DNS monitoring using tools like<\/span><a href=\"https:\/\/dnsspy.io\/\" rel=\"noopener\" target=\"_blank\" rel=\"noopener noreferrer\"> <span>DNS Spy<\/span><\/a><span> or<\/span><a href=\"https:\/\/mxtoolbox.com\/\" rel=\"noopener\" target=\"_blank\" rel=\"noopener noreferrer\"> <span>MXToolbox<\/span><\/a><span>.<\/span><\/li>\n<li><span>Schedule regular SPF record audits (monthly or quarterly).<\/span><\/li>\n<li><span>Check SPF validation status using:<\/span>\n<ul>\n<li><span>nslookup -type=TXT yourdomain.com<\/span><\/li>\n<li><span>MXToolbox SPF Record Lookup<\/span><\/li>\n<\/ul>\n<\/li>\n<li><span>Review email headers of sent emails to verify SPF pass\/fail status.<\/span><\/li>\n<\/ul>\n<p><span>\ud83d\ude80 <\/span><b>Pro tip:<\/b><span> Use SPF flattening to prevent SPF lookup failures and simplify management.<\/span><\/p>\n<h3>Use dedicated subdomains for third-party email senders<\/h3>\n<p><span>Here\u2019s a list of some common services that most of us use<\/span><\/p>\n<ul>\n<li><span>Marketing platforms (Mailchimp, HubSpot, ActiveCampaign)<\/span><\/li>\n<li><span>Transactional email providers (SendGrid, Postmark, Amazon SES)<\/span><\/li>\n<li><span>CRM and customer support tools (Salesforce, Zendesk, Intercom)<\/span><\/li>\n<\/ul>\n<p><span>If all of the above services send emails from the same domain (yourdomain.com), it complicates SPF management, increases the likelihood and risk of SPF failures, or creates deliverability conflicts with other authentication protocols\u2002such as DMARC.<\/span><\/p>\n<p><span>So instead of using yourdomain.com for all email traffic, create subdomains for different purposes.<\/span><\/p>\n<p><span>Here is an example of a subdomain Strategy:<\/span><\/p>\n<ul>\n<li><span>Marketing emails: <\/span><span>mail.yourdomain.com<\/span><span> (SPF for Mailchimp, HubSpot)<\/span><\/li>\n<li><span>Transactional emails: <\/span><span>notify.yourdomain.com<\/span><span> (SPF for SendGrid, Amazon SES)<\/span><\/li>\n<li><span>Support emails: <\/span><span>support.yourdomain.com<\/span><span> (SPF for Zendesk, Intercom)<\/span><\/li>\n<\/ul>\n<p><span>Having separate SPF, DKIM and DMARC\u2002policies for each subdomain minimizes conflicts with authentication and improves deliverability.<\/span><\/p>\n<p><b>\ud83d\ude80 Pro tip:<\/b><span> Separate subdomains also isolate email reputation such that if one email stream (e.g.marketing) runs into deliverability issues, it won\u2019t affect critical business emails (e.g. customer support).<\/span><\/p>\n<h3>Implement DMARC reports to track authentication failures<\/h3>\n<p><span>Even with SPF and DKIM properly configured, issues can still arise if unauthorized servers attempt to send emails on your behalf. This is where DMARC (Domain-based Message Authentication, Reporting &amp; Conformance) helps by:<\/span><\/p>\n<ul>\n<li><b>Enforcing email authentication:<\/b><span> Prevents spoofed emails from being delivered.<\/span><\/li>\n<li><b>Providing real-time email security insights:<\/b><span> Monitors who are sending emails using your domain.<\/span><\/li>\n<li><b>Helping diagnose SPF\/DKIM failures: <\/b><span>DMARC reports show which emails failed authentication and why.<\/span><\/li>\n<\/ul>\n<p><span>DMARC reports show which email senders passed\/failed SPF and DKIM. You can view reports using:<\/span><\/p>\n<ul>\n<li><b>Google Postmaster Tools<\/b><span> (<\/span><a href=\"https:\/\/postmaster.google.com\/\" rel=\"noopener\" target=\"_blank\" rel=\"noopener noreferrer\"><span>https:\/\/postmaster.google.com\/<\/span><\/a><span>)<\/span><\/li>\n<li><b>DMARC Report Analyzers<\/b><span> (<\/span><a href=\"https:\/\/dmarcian.com\/\" rel=\"noopener\" target=\"_blank\" rel=\"noopener noreferrer\"><span>https:\/\/dmarcian.com\/<\/span><\/a><span>)<\/span><\/li>\n<li><b>Easy DMARC<\/b><span> (<\/span><a href=\"https:\/\/easydmarc.com\/\" rel=\"noopener\" target=\"_blank\" rel=\"noopener noreferrer\"><span>https:\/\/easydmarc.com\/<\/span><\/a><span>)<\/span><\/li>\n<\/ul>\n<p><span>If reports show SPF failures from unexpected IPs, you should investigate whether unauthorized senders are trying to impersonate your domain, update your SPF record to include legitimate senders, and gradually increase DMARC enforcement (<\/span><span>p=quarantine<\/span><span> \u2192 <\/span><span>p=reject<\/span><span>).<\/span><\/p>\n<h2><b>How Warmy helps prevent SMTP Error 451 4.7.23<\/b><\/h2>\n<p><span>While SPF authentication is a critical component of email security and deliverability, it\u2019s not enough on its own to ensure emails consistently reach the inbox. Warmy goes beyond SPF by offering a comprehensive suite of tools designed to optimize email deliverability, protect sender reputation, and improve engagement rates.<\/span><\/p>\n<h3>Warmy\u2019s SPF record generator<\/h3>\n<p><span>One of the biggest challenges with SPF is creating and maintaining a correct SPF record. Many senders struggle with formatting errors in SPF records, exceeding SPF\u2019s 10 DNS lookup limit, causing failures, or forgetting to include all email-sending services.<\/span><\/p>\n<p><span>Warmy\u2019s<\/span><a href=\"https:\/\/www.warmy.io\/free-tools\/spf-generator\" target=\"_blank\" rel=\"noopener noreferrer\"> <span>Free SPF Record Generator<\/span><\/a><span> simplifies this process by:<\/span><\/p>\n<ul>\n<li><span>Automatically generating the correct SPF record based on your email service providers.<\/span><\/li>\n<li><span>Optimizing SPF structure to prevent lookup failures.<\/span><\/li>\n<li><span>Ensuring compliance with best practices to avoid SPF misconfigurations.<\/span><\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" alt=\"Screenshot of a webpage titled Free SPF Record Generator. The page has a pastel gradient background. It includes fields labeled Domain, ESP, Email, and SPF value, with a text box for entering a domain and a Next button below.\" height=\"600\" src=\"https:\/\/warmy-blog-wordpress-bucket.s3.amazonaws.com\/wp-content\/uploads\/2025\/03\/11093323\/308shots_so.png\" width=\"800\" title=\"\"><\/p>\n<p><span>Aside from helping prevent SPF-related email blocks, Warmy\u2019s SPF Record Generator ensures recipient mail servers always recognize your domain\u2019s mail servers as legitimate. Simply input your email providers, and Warmy will generate a ready-to-use SPF record that you can copy and paste into your DNS settings.<\/span><\/p>\n<h2><b>Beyond SPF: Warmy\u2019s additional tools for email deliverability<\/b><\/h2>\n<p><span>SPF is only one part of the equation when it comes to email deliverability. To truly maximize inbox placement, Warmy offers a full stack of deliverability tools that work together to enhance your email success.<\/span><\/p>\n<h3>Email warmup tool and advanced seed lists to boost your sender reputation<\/h3>\n<p><span>Many email accounts\u2014especially new or inactive ones\u2014struggle with low sender reputation. This leads to spam filtering and poor deliverability. Warmy\u2019s warmup tool gradually increases email activity, helping to:<\/span><\/p>\n<ul>\n<li><span>improve sender reputation and email trustworthiness.<\/span><\/li>\n<li><span>ensure emails land in the inbox instead of spam.<\/span><\/li>\n<li><span>establish a positive sending history with email providers.<\/span><\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" alt=\"A performance graph on a light orange background shows email activity over time. Two lines represent Sent and Received emails, starting at zero and peaking at about 200. Labels indicate daily, weekly, and monthly metrics.\" height=\"600\" src=\"https:\/\/warmy-blog-wordpress-bucket.s3.amazonaws.com\/wp-content\/uploads\/2025\/03\/11093322\/8shots_so.png\" width=\"800\" title=\"\"><\/p>\n<p><span>At the same time, the email activity mimics natural human behavior, further building trust with email service providers. Meanwhile, Warmy\u2019s <\/span><a href=\"https:\/\/www.warmy.io\/product\/seed-list\" target=\"_blank\" rel=\"noopener noreferrer\"><span>advanced seed lists<\/span><\/a><span> are genuine email addresses that simulate real human behavior. Emails are opened, read, scrolled through, and clicked, further reducing the chances of landing in spam. Plus, if emails go to spam, they are manually removed and marked as important to improve future deliverability.<\/span><\/p>\n<h3>DMARC Record Generator to strengthen email authentication<\/h3>\n<p><span>SPF works best when combined with DKIM and DMARC, which provide extra layers of authentication to:<\/span><\/p>\n<ul>\n<li><span>Prevent email spoofing and phishing attacks<\/span><\/li>\n<li><span>Ensure email integrity and authenticity<\/span><\/li>\n<li><span>Improve overall deliverability<\/span><\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" alt=\"A DMARC Record Generator interface on a gradient background. The form includes radio buttons for Domain, ESP, Email, and DMARC value. A text input field asks for a domain, with a Next button below.\" height=\"600\" src=\"https:\/\/warmy-blog-wordpress-bucket.s3.amazonaws.com\/wp-content\/uploads\/2025\/03\/11093321\/848shots_so.png\" width=\"800\" title=\"\"><\/p>\n<p><span>Warmy offers a free<\/span><a href=\"https:\/\/www.warmy.io\/free-tools\/dmarc-generator\" target=\"_blank\" rel=\"noopener noreferrer\"> <b>DMARC Record Generator<\/b><\/a> <span>unauthorized senders from misusing your domain.<\/span><\/p>\n<h3>Email deliverability test and dashboard to monitor domain health<\/h3>\n<p><img loading=\"lazy\" decoding=\"async\" alt=\"Email security assessment interface showing a score of 9 (High) with validation statuses for SPF, DKIM, DMARC, rDNS, A-Record, and MX-Record. The last test was conducted at 10:30 AM on October 24, 2024.\" height=\"600\" src=\"https:\/\/warmy-blog-wordpress-bucket.s3.amazonaws.com\/wp-content\/uploads\/2025\/03\/11093321\/802shots_so.png\" width=\"800\" title=\"\"><\/p>\n<p><span>Warmy\u2019s free <\/span><a href=\"https:\/\/www.warmy.io\/free-tools\/email-deliverability-test\" target=\"_blank\" rel=\"noopener noreferrer\"><span>email deliverability test<\/span><\/a><span> is a gateway to the inner workings of your email deliverability. It helps users get data on the following:<\/span><\/p>\n<ul>\n<li><b>Inbox placement testing: <\/b><span>Know where your emails land (Inbox, Spam, Promotions tab) across major providers like Gmail, Outlook, and Yahoo! and what percentage lands in which folder.<\/span><\/li>\n<li><b>Blacklist monitoring: <\/b><span>Find out if your sending IP or domain is blacklisted, which could trigger SMTP errors and delivery failures.<\/span><\/li>\n<li><b>SPF, DKIM, DMARC verification:<\/b><span> Ensure proper authentication to reduce deferrals and enhance sender credibility.<\/span><\/li>\n<\/ul>\n<h2><b>Warmy\u2014the ultimate email deliverability solution<\/b><\/h2>\n<p><span>With Warmy, you don\u2019t have to be an email authentication expert to achieve great deliverability. Warmy ensures that your emails consistently land in inboxes\u2014helping you avoid SMTP errors, improve engagement, and maximize email success.<\/span><\/p>\n<p><span>Ready to take control of your email deliverability? <\/span><a href=\"https:\/\/www.warmy.io\/signup\" target=\"_blank\" rel=\"noopener noreferrer\"><span>Try Warmy today<\/span><\/a><span> and ensure your emails pass authentication checks with flying colors.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"<p>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) [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":4719,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[104],"tags":[],"class_list":["post-4031","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-email-deliverability"],"acf":[],"lang":"en","translations":{"en":4031},"pll_sync_post":[],"_links":{"self":[{"href":"https:\/\/www.warmy.io\/blog\/wp-json\/wp\/v2\/posts\/4031","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.warmy.io\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.warmy.io\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.warmy.io\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.warmy.io\/blog\/wp-json\/wp\/v2\/comments?post=4031"}],"version-history":[{"count":1,"href":"https:\/\/www.warmy.io\/blog\/wp-json\/wp\/v2\/posts\/4031\/revisions"}],"predecessor-version":[{"id":5783,"href":"https:\/\/www.warmy.io\/blog\/wp-json\/wp\/v2\/posts\/4031\/revisions\/5783"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.warmy.io\/blog\/wp-json\/wp\/v2\/media\/4719"}],"wp:attachment":[{"href":"https:\/\/www.warmy.io\/blog\/wp-json\/wp\/v2\/media?parent=4031"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.warmy.io\/blog\/wp-json\/wp\/v2\/categories?post=4031"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.warmy.io\/blog\/wp-json\/wp\/v2\/tags?post=4031"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}