SuperMailOS
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Is your email set up to land in the inbox?

Enter your domain and we'll check the DNS records that decide whether your mail is trusted (SPF, DKIM, DMARC, MX and MTA-STS) and tell you, in plain English, what to fix.

01 The records

What each record means.

Five minutes of DNS reading will make the rest of this make sense. Here's what your domain is actually telling the world.

SPF says who can send

An SPF record is a single line in your DNS that lists every server allowed to send email as your domain: your mail host, your newsletter tool, your helpdesk. Receivers check incoming mail against that list. No SPF, or too many SPF lookups, and legitimate mail starts failing the first trust check.

DKIM proves it's really you

DKIM signs every outgoing message with a cryptographic key; the matching public key lives in your DNS. The signature covers the content, so it also proves nothing was tampered with in transit. It's the strongest authenticity signal receivers have, and the one most self-hosted setups get wrong.

DMARC ties them together

DMARC tells inbox providers what to do when SPF or DKIM fails (nothing, quarantine, or reject) and sends you reports showing exactly who is sending as your domain, including spoofers. Publishing a policy is what turns two DNS records into actual protection against impersonation.

MTA-STS enforces TLS

MTA-STS is a DNS record plus a small policy file that tells other mail servers to only connect to you over encrypted TLS, never fall back to plaintext. Without it, mail between servers can be silently downgraded. With it, encryption becomes mandatory for everyone sending you mail.

02 Questions

Common questions.

Something else? Write to us — a real person answers, usually the same day.

Talk to us
What does this email checker actually test?+
It looks up the DNS records that decide whether your mail is trusted (SPF, DKIM, DMARC, MX and MTA-STS) and explains, in plain English, what each one says and what to fix. No signup, nothing stored.
Why is my email going to spam?+
Usually one of three things: a missing or broken authentication record (SPF, DKIM, or DMARC), a young domain or IP with no sending reputation yet, or content and engagement patterns that look like spam. The checker rules the first one in or out in seconds.
Do I need all three records — SPF, DKIM, and DMARC?+
Yes. SPF authorizes your servers, DKIM proves the message is genuinely yours and untampered, and DMARC tells receivers what to do when either check fails, and reports back who's sending as you. Major providers like Gmail and Microsoft now effectively require all three for bulk senders.
How do I fix a failed check?+
Every failed check comes with the exact DNS record to add or change. If you'd rather never touch DNS at all, that's what SuperMailOS does: bring your domain and the records are generated, published, and monitored for you.

03 More free tools

Keep checking.

Each tool answers one question about a domain's email. All free, no signup.

All free tools ▶
Reputation→

Email deliverability test

Send a real email to a test address and get a score out of 10, with every fix ranked by impact.

Reputation→

Email health score

Authentication, blocklists, routing and domain age combined into one A–F grade.

Authentication→

DMARC checker

Every DMARC tag explained, report destinations verified, and the next step toward p=reject.

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