TL;DR: Warmy.io and Mail-Tester both help your email reach the inbox, but they solve different problems. Mail-Tester is a free tool that sends one message through SpamAssassin and returns a spam score out of 10 along with configuration checks. Warmy.io is an AI-powered platform that warms up your mailbox, tests real inbox placement across Gmail, Outlook, and Yahoo, and monitors sender reputation over time. Choose Mail-Tester for a fast pre-send check. Choose Warmy when you need to actively improve and defend deliverability.
Roughly one in six emails never reaches the inbox. Warmy’s State of Email Deliverability report (2025) put the average global inbox placement rate at 83.5%, which means a meaningful share of legitimate mail lands in spam or disappears entirely. Before you blame your copy, it helps to know whether the problem is your message, your authentication, or your sender reputation. Two tools come up constantly in that diagnosis: Mail-Tester and Warmy. You can start by running Warmy’s free Email Deliverability Test to see where your mail is landing right now.
Warmy is an AI-driven email warmup and deliverability platform that builds sender reputation and improves inbox placement, while Mail-Tester is a free spam-score checker that grades one email at a time. This guide compares how each tool works, what it measures, what it costs, and when to reach for one over the other. The short version is that they operate at different layers of the same problem, and many teams use both.
What is Mail-Tester and how does it work?
Mail-Tester is a free web tool that grades the spammyness of a single email. It runs your message through SpamAssassin, a widely used open-source spam filter, and returns a score out of 10.
The workflow is simple:
- Mail-Tester generates a unique email address each time you open the tool.
- You send your email to that address from your normal email or newsletter software.
- Mail-Tester analyzes the message, your mail server, and your sending IP, then grades it.
- You get a report scored out of 10 that shows what is configured correctly and what needs work.
The score is the reversed SpamAssassin score, so a higher number is a better result; a perfect result is 10 out of 10. The report checks your SPF and DKIM setup, flags spammy content and formatting, and looks up your sending server against blacklists. Mail-Tester also links out to free authentication tools, including SPF, DKIM, DMARC, and BIMI checkers powered by EasyDMARC.
On the free web interface, you can run up to 3 tests every 24 hours, and each result remains accessible for 7 days. Creating an account extends result storage to 30 days and unlocks add-ons. A JSON API and iframe embedding are available on paid plans, along with white-label result pages, usage statistics, and ad-free reports.
One limitation matters for anyone treating the score as a guarantee. A perfect 10 out of 10 measures configuration and content quality, not whether your email actually lands in the inbox. Spam filters differ by provider and adapt to each recipient, and some users have reported different scores for the same message from different sending locations. Mail-Tester is a strong pre-send sanity check, not a live placement report.
Warmy.io: What it is and how it works
Warmy is an AI-driven email warmup and deliverability platform that helps businesses build sender reputation, improve inbox placement, and scale outreach safely. Where Mail-Tester grades one message, Warmy works continuously on the underlying reputation that decides whether your mail reaches the inbox at all. According to Warmy, more than 35,000 businesses and 650,000 domains have used the platform to improve deliverability.
Its core capabilities include:
- AI-powered email warmup run by an engine called Adeline. It gradually increases sending volume and simulates genuine engagement by opening, reading, scrolling, clicking, replying to, and recovering messages from spam. The platform handles up to 5,000 warmup emails per day and works across more than 30 languages.
- A free Email Deliverability Test that sends to real seed inboxes across Gmail, Outlook, Yahoo, iCloud, and Zoho, plus marketing systems like Mailchimp, SendGrid, HubSpot, and Salesforce. It reports the exact percentage of mail reaching the inbox, spam, or unreceived, and checks blacklists and authentication.
- Free record generators for SPF and DMARC, plus a Template Checker that scans content for spam triggers before you send.
- Ongoing deliverability monitoring with domain health scores, blacklist tracking, and a direct Google Postmaster Tools integration.
Warmy is SOC 2 Type II compliant and reports customer results of 2.3x higher open rates and a 22.5% lift in email channel conversion rates. If you are weighing broader options, Warmy also publishes a guide to the best email warmup and deliverability tools.
Warmy vs. Mail-Tester: Side-by-side comparison
Here is how the two tools line up across the factors that matter most.
| Factor | Warmy.io | Mail-Tester |
|---|---|---|
| Primary purpose | AI email warmup and full deliverability platform | Free spam-score and configuration checker |
| What it measures | Real inbox placement, sender reputation, blacklists, authentication | SpamAssassin spam score out of 10, plus server, IP, and content checks |
| Email warmup | Yes, automated AI warmup (Adeline) | No |
| Deliverability test | Sends to real seed inboxes across major providers with inbox, spam, and unreceived breakdown | Indirect; one email graded for spam-likelihood, not live placement |
| Blacklist checks | Ongoing monitoring | Included in each report |
| SPF, DKIM, DMARC | Checks and generates records | Checks existing SPF and DKIM; generator links via EasyDMARC |
| Google Postmaster | Native integration | No |
| Free option | Free deliverability test, no signup; 7-day product trial | Free web test, 3 per 24 hours, results kept 7 days |
| API | Yes | Yes, on paid plans |
| Languages | Warmup and interface in 30+ languages | Interface in 20+ languages |
| Best for | Actively improving and monitoring deliverability over time | A fast, free pre-send configuration and spam-score check |
Deliverability testing, warm-up, and authentication compared: Warmy vs. Mail-Tester
Spam score vs. real inbox placement
This is the core difference. Mail-Tester tells you how a single message scores against SpamAssassin and whether your DNS records are set up correctly. That is useful, but a clean score does not prove your email reaches the inbox, because each provider filters differently. Warmy’s deliverability test answers the placement question directly by sending to real seed inboxes and showing the share that lands in the inbox, spam, or nowhere at all across Gmail, Outlook, Yahoo, and more.
Warm-Up: The layer Mail-Tester does not cover
Mail-Tester has no warm-up feature, and it does not claim to. If your domain is new or your reputation is damaged, a spam score cannot fix it. Warmy’s automated warmup gradually builds sending history and positive engagement so mailbox providers learn to trust your domain. This is the part of the deliverability problem that a one-time test cannot solve, and it is the main reason teams pair a checker with a warm-up platform.
Authentication tools: Check vs. create
Both tools verify SPF and DKIM. Mail-Tester reports on the records you already have and links to external generators. Warmy checks SPF, DKIM, and DMARC and gives you free generators to build the correct records when they are missing or misconfigured. For anyone less comfortable with DNS, the ability to generate a valid record inside the same platform removes a common point of failure.
Pro Tip: Run Mail-Tester and Warmy’s free Email Deliverability Test on the same message. Mail-Tester catches configuration and content problems before you send, and Warmy shows where that message actually lands across Gmail, Outlook, and Yahoo. Fix the Mail-Tester issues first, then use Warmy to confirm the inbox result and keep it steady over time.
Pricing: Warmy vs. Mail-Tester
Mail-Tester is free for occasional use, with paid volume for teams. Monthly subscriptions, excluding VAT, run $10 for 50 tests, $25 for 500 tests, $80 for 2,000 tests, and $250 for 7,500 tests. One-time packs run from $5 for 10 tests up to $700 for 15,000 tests, and paid plans are where the API, iframe, and white-label features live. You can review current rates on the Mail-Tester pricing page.
Warmy does not publish fixed pricing. It uses custom per-mailbox plans positioned by sender type, and interested users book a demo for a quote. The practical takeaway is that Mail-Tester is priced per test, while Warmy is priced per mailbox and includes the warm-up and monitoring that a test-only tool does not.
Reviews and ratings
Third-party ratings as of 2026:
- Warmy.io: 4.8 on G2 (498 reviews), 4.9 on Capterra, and 4.0 on Trustpilot. Reviewers praise the warmup engine, ease of setup, and support, while the most common criticism is per-mailbox pricing at scale.
- Mail-Tester: 4.2 on G2 (10 reviews), 3.3 on Capterra (12 reviews), and 3.5 on Trustpilot (11 reviews). Reviewers value the speed and simplicity, while the recurring complaint is score inconsistency and the reminder that a high score is not a delivery guarantee.
The rating gap partly reflects scope. Mail-Tester is a lightweight utility with a small review base, and Warmy is a full platform with a much larger one. If you want a deeper platform comparison, see Warmy vs. Smartlead.
Which tool should you choose?
Pick Mail-Tester when you want a quick, free way to check a single email for spam triggers and DNS mistakes before sending. It is fast, requires no account for occasional use, and it is genuinely helpful for catching configuration errors.
Pick Warmy when you need to fix and defend deliverability rather than just measure it. Warm-up, real inbox placement testing, blacklist monitoring, and record generators address the reputation and infrastructure problems that a spam score can flag but cannot solve. For cold outreach and high-volume sending, that ongoing work is what keeps mail in the inbox.
In practice, the strongest setup uses both. Run Mail-Tester for a pre-send check, and run Warmy to build, test, and protect your sender reputation over time.
Ready to see where your emails land and keep them in the inbox? Book a free deliverability consultation.
