What supermail covers
- A real SMTP message, not a DNS-only form
- Cryptographic DKIM verify plus DNS key publication
- SPF record and SPF evaluation against the sending IP
- DMARC policy, rua/ruf, and alignment with From
- MTA-STS, TLS-RPT and BIMI DNS checks (optional)
- DNSBL, PTR↔HELO, HELO A, content and MIME
- DNS wizard: ready TXT drafts for the From domain
- Export: JSON and Print/PDF; AI and mail-admin briefs
- Findings filter (All / Errors / Passed), 23 UI languages
How to use
- Copy the test address (you can keep or share the ?i=… link)
- Send a message from your server, ESP or normal mailbox
- Wait 10–60 seconds — keep the tab open
- Read the grade, findings filter, DNS wizard and headers
- Download JSON, print to PDF, or take the AI / admin brief
Deliverability tips
Filters look at DNS, the server name and the wording. Fix auth (SPF/DKIM/DMARC alignment) and content together — one TXT record is not enough.
Practice
- Sign DKIM with the same domain as From; the signature must crypto-verify
- Never use +all in SPF; the sending IP should evaluate to pass
- DMARC: p=none + rua, then quarantine → reject; watch alignment
- IP PTR should match HELO/EHLO; HELO needs a working A record
- Optional: MTA-STS and TLS-RPT; BIMI after enforce DMARC
- Copy TXT drafts from the DNS wizard and fill in your selector/keys
When you need it
- Before a bulk campaign or transactional mail launch
- After changing ESP, Postfix/Exim or the sending IP
- When Gmail, Mail.ru or Outlook file mail as spam
- Checking SPF/DKIM/DMARC alignment and IP reputation (DNSBL)
- Gather DNS records and hand an admin or AI a ready brief
FAQ
Where do I send mail?
To the unique …@supermail.dmosk.net address on the page — from your SMTP, ESP or a normal mailbox.
What exactly do you check?
Crypto DKIM verify, SPF record and SPF against the connecting IP, DMARC (policy, rua/ruf, alignment with From), DKIM DNS key, MX, MTA-STS / TLS-RPT / BIMI, DNSBL, PTR↔HELO and HELO A, content and MIME, Authentication-Results, Received/TLS, List-Unsubscribe, ARC and more. The report includes an A–F grade, spam score, DNS wizard, headers, JSON and Print/PDF.
How is the grade calculated?
The /100 grade and the heuristic spam score are different scales. Grade: start at 100, subtract by severity (critical −35, high −20, medium −10, low −5). Spam score sums small per-check weights; it does not have to match points taken from 100.
Do you verify DKIM crypto and SPF against the IP?
Yes. We cryptographically verify DKIM and evaluate SPF for the connecting IP and MAIL FROM / From domain, plus DKIM key publication and DMARC alignment.
What is the DNS wizard?
The report includes TXT drafts (SPF, DMARC, DKIM, MTA-STS, TLS-RPT, BIMI) for the From domain. Copy them and fill in your selector, keys and includes before publishing DNS.
How do I export the report?
Use Download JSON and Print / PDF on the report. There are also two Markdown briefs: an AI agent task (no live rescans) and a plain mail-admin checklist.
How long do the inbox and report link live?
Waiting for mail lasts about 30 minutes. A ready report via ?i=… stays available about 7 days, then is removed. See the Privacy page for details.
Is there a public API?
Yes: POST /api/v1/inbox and GET /api/v1/inbox/{id}. The contract is in the GitHub README and service docs.
Which languages are supported?
23 UI locales. Finding copy is localized by check code; Markdown briefs are Russian or English depending on the page language.
Is this a mail-tester clone?
Same flow: inbox → message → report. The checks, wording, DNS wizard, export and two briefs are ours; we do not ship full SpamAssassin.
Is it free?
Yes.