Mail-tester.com - email deliverability testing service - 2026

Published: 2026-08-04

Mail-Tester (mail-tester.com) is a popular online service for checking the quality of email sending and assessing its deliverability. The main purpose of the service is to help you understand why emails from your mail server or email marketing platform land in the "Spam" folder instead of the "Inbox."

The service works on a simple principle: it generates a random test address, you send a test message to it, and then it performs a comprehensive analysis of that message across dozens of parameters — from classic authentication records (SPF, DKIM, DMARC) to the reputation of the IP address, HTML content, links, and body text. The result is a score from 0 to 10 with a detailed report and specific recommendations for every check.

How Mail-Tester works

The workflow is straightforward and does not require installing any software.

Open the main page at mail-tester.com.
The service generates a unique random address in the form your-session-id@mail-tester.com.
Send a test email to that address from your mail server, SMTP relay, or email marketing platform (Mailcow, Postal, MailWizz, Mautic, Postfix, Exim, etc.).
Shortly afterwards the message is processed by the service.
Click the Check your score button (or simply refresh the page).
Get a detailed report with a score broken down into separate blocks, each containing an explanation and recommendations.

One of the key features is that the address is tied to a specific checking session: you see the results of exactly the message you sent. This makes it possible to iteratively fix configuration issues and re-test until the score becomes maximum.

What Mail-Tester checks

After analyzing the message, the service produces a report covering the following aspects.

Check	What it means
SpamAssassin Score	The likelihood that the message will be recognized as spam. The lower the SpamAssassin score, the better.
SPF	Verifies that your mail server is allowed to send mail on behalf of the sender's domain.
DKIM	Verifies the presence and validity of the digital signature that authenticates the message with a cryptographic key.
DMARC	Verifies the domain authentication policy — instructions to the receiver about what to do with messages failing SPF/DKIM.
DNS records	Correctness of the mail domain settings: MX, TXT, CNAME and related resource records.
PTR (Reverse DNS)	Presence of a reverse DNS record for the sending IP address.
HELO/EHLO	Correctness of the name that the SMTP server announces when establishing a connection.
Blacklists (DNSBL/RBL)	Checks whether the server IP address appears in public spam databases.
HTML of the message	Detection of errors and inconsistencies in the HTML markup affecting rendering and scoring.
Links	Detection of suspicious, shortened, or broken links, and validation of link domains.
Attachments	Checking attached files for signs of potential danger.
Message text	Analysis of the text content for words and patterns typical of spam.

SpamAssassin Score

SpamAssassin is a widely used open-source spam-filtering tool. Mail-Tester runs your message through SpamAssassin rules and shows the number of points scored. If the score is below the threshold (usually 5), the message is considered not overly spammy. A high score means the message exhibits typical spam indicators: spam trigger words, suspicious links, reputation problems, incorrect HTML markup, and so on.

The SpamAssassin report shows not only the final score but also the individual rules that fired, so you can see exactly which factor added "weight" to your message.

SPF (Sender Policy Framework)

SPF is a TXT record in DNS that lists the IP addresses or servers allowed to send mail on behalf of your domain. A message from a domain whose legitimacy is confirmed by an SPF record is more likely to reach the Inbox.

A typical SPF record looks like this:

v=spf1 a mx ip4:192.0.2.10 include:relay.example.com -all

v=spf1 — the record version;
a — allows sending from IP addresses matching the domain's A records;
mx — allows sending from the domain's mail servers (MX records);
ip4:... — explicitly lists an allowed IPv4 address;
include:... — delegates part of the rules to another domain (commonly used by email marketing platforms);
-all — a hard fail for all other addresses (the recommended terminating mechanism).

Mail-Tester will show whether the IP address of the server that delivered the test message matches the addresses allowed by your SPF record.

DKIM (DomainKeys Identified Mail)

DKIM is a mechanism for cryptographically signing messages. The sending server signs the message with a private key, and the receiver validates the signature using a public key published in DNS as a TXT record under a selector. DKIM allows the receiver to make sure the message was not altered in transit and was genuinely sent from your server.

Mail-Tester checks:

the presence of the DKIM key in DNS;
the correctness of the signing algorithm;
the match between the signer domain (d=) and the sender domain;
key validity and expiration.

The service also offers a separate free tool, the SPF & DKIM Checker (/spf-dkim-check), which lets you validate SPF and DKIM records without sending a message.

DMARC (Domain-based Message Authentication, Reporting, and Conformance)

DMARC builds on the results of SPF and DKIM and tells the receiving server what to do with messages that fail authentication. The DMARC record also allows receivers to send reports about incoming mail, so you can monitor whether your domain is being abused (for example, in phishing).

The DMARC policy has three levels:

none — monitoring only; messages that fail authentication are still delivered, but reports are sent to the domain owner;
quarantine — messages that fail authentication are sent to the spam folder;
reject — messages that fail authentication are rejected outright.

An example DMARC record:

v=DMARC1; p=quarantine; rua=mailto:dmarc@example.com; ruf=mailto:forensic@example.com; fo=1

Mail-Tester verifies the presence of the DMARC record, the correctness of the syntax, and the consistency of the policy with the current SPF and DKIM setup.

PTR (Reverse DNS)

The reverse DNS record (PTR) maps an IP address to a hostname. Many major mail providers require the PTR record to match the name that the server announces in HELO/EHLO. A missing PTR record or a mismatch is one of the most common reasons for emails landing in spam, especially when sending from VPS instances and cloud platforms.

Mail-Tester shows which name is returned for your IP address and whether it matches the HELO name of the server. If the PTR is missing, the report will suggest requesting it from your hosting provider.

HELO/EHLO

When establishing an SMTP connection, your server identifies itself with a HELO or EHLO string. An incorrect name (for example, a local value like localhost or an IP address instead of a hostname) is a red flag for spam filters. The ideal situation is when the HELO name matches the PTR record of the sender's IP and the hostname of the machine.

Blacklists (DNSBL/RBL)

Mail-Tester checks your IP address and your DNS servers against several public blacklists (DNSBL/RBL). If your address appears on any of these lists, your sending reputation suffers significantly. The report names the list on which the address was found, so you can initiate the delisting procedure.

Keep in mind that ending up on a blacklist is often a symptom of other problems: weak authentication settings, a high volume of spam complaints, or a compromised server.

HTML, links, attachments, and message text

The content of the message is also analyzed for spam indicators:

HTML markup — the service checks for markup errors, the absence of a plain-text alternative, the use of table-based layouts and CSS styles typical of spam, and an excessively high image-to-text ratio.
Links — it counts the number of links, checks for URL shorteners, links to suspicious domains, and mismatches between the visible link text and the actual URL.
Attachments — attachment types are evaluated; for example, ZIP archives, executables, scripts (JS, VBS), and documents with macros raise immediate suspicion.
Text — spam trigger words and phrases ("free", "you have won", "urgent attachment", excessive use of capital letters and exclamation marks) and the overall message structure are analyzed.

Interpreting the score

The final score ranges from 0 to 10.

10/10 — everything is technically configured perfectly: authentication works, reputation is fine, and the content raises no suspicion.
8–9/10 — there are minor remarks that are recommended to fix for stable deliverability.
Below 8 — the configuration should be seriously improved, otherwise the risk of emails landing in spam significantly increases.

It is important to understand the limit of the service: even a 10/10 score does not guarantee delivery to the Inbox. Modern email giants (Gmail, Outlook, Yahoo) account for many additional factors:

the reputation of your domain and IP address;
sending history and volume;
recipient behavior (opens, clicks, replies, "report spam" complaints);
bounce rates and engagement in campaigns.

Mail-Tester measures the technical and content side, but it cannot measure overall reputation and behavioral signals. Therefore, a high score is a necessary but not sufficient condition for Inbox delivery.

Additional tools offered by the service

Beyond the main test, the Mail-Tester website provides a set of free helpers for working with DNS and authentication:

SPF & DKIM Checker (/spf-dkim-check) — validates existing records without sending an email;
SPF Checker (/spf/) — detailed validation of a domain's SPF record;
Generators from EasyDMARC — generators for SPF, DKIM, and DMARC records;
DMARC Checker / DKIM Checker / BIMI Checker — validation of the corresponding DNS records;
Domain Scanner — scans a domain for mail and DNS issues.

Mail-Tester also has a paid managed version (Manager), an API for automating checks, and a blog focused on email deliverability. The website is translated into dozens of languages, including Russian.

Who benefits from Mail-Tester

The service is primarily useful for:

administrators setting up their own SMTP servers (Postfix, Exim, Dovecot, and combinations);
those deploying their own email marketing platforms (Mailcow, Postal, MailWizz, Mautic, Roundcube, Listmonk, and others);
marketers and developers working with email marketing who want to make sure messages reach the Inbox;
anyone who suspects that messages are lost or sent to spam because of incorrect SPF, DKIM, DMARC settings or reputation issues;
system engineers when migrating mail services or changing IP addresses or providers.

For people building a mail server from scratch, Mail-Tester is one of the first tools for verifying configuration correctness before real sending begins.

Common problems and how to fix them

No PTR record — contact your hosting provider and request a reverse DNS record for your IP, consistent with the hostname.
SPF uses ~all (softfail) or lacks -all — replace with -all if all legitimate senders are listed in the record.
Multiple SPF records — merge them into a single record, otherwise SPF becomes invalid (PermError).
No DKIM — enable signing in your MTA (for example, OpenDKIM for Postfix) and publish the public key in DNS.
No DMARC — add a record with at least a none policy to collect reports, then gradually raise it to quarantine/reject.
IP on a blacklist — find the source of the listing, eliminate the cause, and submit a delisting request.
Non-descriptive HELO name — configure a correct hostname with a fully qualified domain name.
Little text, many images — add a text version of the message and balance the text-to-image ratio.
Spam trigger words in subjects and body — rephrase subject lines and remove aggressive marketing wording.
Sending from an IP with questionable history — use dedicated IPs or reputation warm-up services.

Limitations of the service

Mail-Tester is not a silver bullet: it evaluates one specific message at one specific point in time. Reputation and behavioral factors remain beyond its scope.
The result depends on how the filters of major providers behave in your region and on the individual settings of recipients.
A 10/10 score measures the technical "cleanliness" of a message, not actual delivery to a particular user.
For a fuller picture of deliverability, you should additionally use reputation monitoring services, seed tests (for example, sending to controlled Gmail/Outlook inboxes), and the statistics of your own sending system.

Conclusion

Mail-Tester is an indispensable free tool for diagnosing the health of your email sending setup. It quickly provides an objective picture across all key technical parameters: SPF, DKIM, DMARC, PTR, HELO, blacklists, and message content. Thanks to the clear 0–10 score and concrete recommendations, the service suits both beginners setting up mail for the first time and experienced administrators tuning high-volume sending systems.

The main rule when using Mail-Tester is to treat its high score as a necessary condition, not a guarantee of delivery. Real deliverability consists of technically correct configuration, stable reputation, and high-quality, relevant content that recipients are willing to engage with.

Summary

Mail-Tester is a free service that tests the "spamminess" and deliverability of email messages. To run a test, you send a message to a generated address, after which the service analyzes SpamAssassin, SPF, DKIM, DMARC, DNS and PTR records, HELO/EHLO, blacklists, HTML, links, attachments, and text, producing a score from 0 to 10. The service is especially useful when setting up your own SMTP servers (Postfix, Exim) and email marketing platforms (Mailcow, Postal, MailWizz, Mautic). A high score does not guarantee Inbox delivery, because Gmail and Outlook also account for domain and IP reputation, sending history, and recipient behavior.

Links

×