Mail-tester says 10/10 but the mail lands in spam: what it misses
A 10/10 on mail-tester means a default SpamAssassin run found your setup and content clean. It cannot see reputation or engagement, which drive Gmail placement.
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You sent a test to mail-tester.com, got a perfect 10/10, and your real email still lands in spam at Gmail or Outlook. The test is not broken. It answers a narrower question than the one you are asking.
Mail-tester is a free tool that scores one message. Per its own FAQ, the score comes from SpamAssassin, a default out-of-the-box install, applied to your message, your mail server and your sending IP. A 10/10 means that engine found nothing to complain about. Mailbox providers run their own filters on their own data, and the same FAQ notes that a perfect score does not guarantee inbox placement.
What does a mail-tester score actually measure?
It measures the message and the setup in front of it: content patterns, whether authentication is in place, and whether the sending IP appears on common blocklists. It reads one message at one moment.
That is useful. A 4/10 usually points to something you can fix in minutes, such as a missing DKIM signature or a broken HTML structure. Treat the tool as a lint check for a message. A lint check passing does not mean the program works.
Why can a 10/10 message still go to spam?
Because the signals that decide placement at large providers are mostly not in the message. Google's sender guidelines say plainly that they cannot guarantee messages pass Gmail's spam filters and that some legitimate messages may be marked as spam. They also name the inputs that matter beyond authentication: user spam reports lower a domain's reputation over time, and on a shared IP the activity of every sender affects all of them. Messages from an address in the recipient's contacts are less likely to be marked as spam.
A single-message test sees none of this. The table lists what a 10/10 cannot tell you.
| Signal | Seen by mail-tester? | Why it matters |
|---|---|---|
| Domain reputation | No | Built from history and recipient reactions, not from one message |
| IP reputation, shared or dedicated | Only blocklist status | A shared IP carries other senders' behavior |
| Engagement (opens, replies, deletes, spam reports) | No | Recipient actions shape each mailbox's filter |
| Domain age and sending history | No | A brand-new domain has no track record to trust |
| Provider-specific filtering | No | Gmail, Outlook and Yahoo use their own models |
| Volume and sending pattern | No | Sudden spikes look different from steady sending |
Practitioner threads show the same pattern. In one iRedMail forum thread, a sender with a 10/10 landed in spam at Gmail and Comcast, and the maintainer's answer was that those providers do not use the same data as mail-tester. The thread never identified a specific cause, which is typical: the test cannot show the cause, so the diagnosis has to come from somewhere else.
Is your domain simply too new?
A new domain with a perfect score is the most common version of this problem. Filters have no history to trust, so even clean mail gets cautious treatment. The fix is time and a careful start, not more testing: begin with your most engaged recipients and grow steadily, as described in warming up a brand-new sending domain.
If the domain is old but has been quiet for months, the same logic applies in a milder form. See restarting a quiet sending domain after months of silence.
What should you check after the score passes?
Work from the cheapest check to the slowest. The order below avoids guessing.
- Read the real headers of a spam-foldered copy. Open the message that landed in spam at the recipient and look for
Authentication-Results. Confirm SPF, DKIM and DMARC pass for the domain you intended, and that the From domain aligns. Mail-tester tests the message it received, which may not be the path your real mail takes. Use the Authentication-Results header guide to read it. - Check domain reputation at the provider. If you send to Gmail users, Google Postmaster Tools is the only direct view of how Gmail rates your domain. At low volume it may show no data, which is itself information: you have no established reputation yet.
- Check blocklists for your domain and IP. Mail-tester looks at the IP; also check the domain and any link domains in the message. If you are listed, follow the blocklist delisting playbook.
- Look at who you are sending to. Mail to people who did not expect it, who never opened your last five messages, or whose addresses are old produces the complaints and non-engagement that filters read as junk.
- Compare the failing mailbox with a working one. If Gmail delivers and Outlook does not, you are looking at a provider-specific problem, not a content problem. Test with real, consenting recipients at each provider.
- Use seed tests with their limits in mind. Panel and seed-list tools show placement for test accounts, not your users; inbox placement testing covers what to trust.
What does a healthy test routine look like?
Use mail-tester before a launch or after a DNS change, to catch obvious mistakes. Then judge delivery by what real recipients experience.
- Send a real message to a few real mailboxes at Gmail, Outlook and Yahoo before any large send, and check where it lands.
- Ask one or two recipients who landed in spam to mark it "not spam" and reply. Replies and contact-list additions are strong positive signals according to Google's guidance above.
- Watch bounces and complaint rates over days, not minutes. Both Google and Yahoo tell bulk senders to keep spam complaints below 0.3%, and Google's page also advises staying well under that, below 0.10%.
- Re-test after changes, one change at a time, so you know what moved the result.
The free tier is also small. At the time of writing the FAQ says three tests per 24 hours, and each new message to the same test address deletes the previous report, so save a copy of any result you want to compare against later.
Does this apply to Koltrix?
Koltrix signs outbound mail with a per-domain DKIM key and walks you through SPF and DMARC when you verify a domain, so the authentication checks that mail-tester runs should pass once setup is complete. That is the part a tool can verify. Reputation is the part that builds from your own sending behavior, and no sender can buy it with a configuration change.
Bottom line
A 10/10 on mail-tester means your message and setup look clean to a default SpamAssassin install. It says nothing about domain reputation, engagement, domain age or how Gmail and Outlook rate you. When a perfect score still ends in spam, stop re-running the test, read the headers of a real spam-foldered message, check Postmaster Tools and blocklists, and review who you are sending to. For the general flow after authentication passes, continue with passing authentication but still in spam.
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