Mail Domain Check

Live RFC 8461 publication check

MTA-STS policy checker

Verify the DNS announcement and exact HTTPS policy publication, then see policy mode, cache lifetime, MX pattern count, and companion TLS-RPT status.

Live DNS + HTTPS

INPUT

Mail domain

The domain is sent to this service for public DNS and HTTPS checks. Free analytics retain an irreversible domain hash and aggregate metrics, not the raw value.

Enter the organizational domain that receives mail. Policy discovery uses _mta-sts.example.com and https://mta-sts.example.com/.well-known/mta-sts.txt.

RESULT

Published policy

No domain checked

Enter a mail domain to inspect its STSv1 announcement, HTTPS policy, and TLS reporting record.

Three separate states

Publication is more than one DNS record

Announcement_mta-sts TXT

RFC 8461 requires one v=STSv1 record with an alphanumeric policy id. Multiple STSv1 records prevent policy discovery.

Policy endpointFixed HTTPS path

The policy must be available at the exact /.well-known/mta-sts.txt path. Redirects are not followed, and the response is bounded to 64 KB.

Sender behaviorCached independently

A live check cannot see every sender's cached policy. A previously cached policy can continue to affect delivery until its max_age expires.

Primary references: RFC 8461 SMTP MTA Strict Transport Security and RFC 8460 SMTP TLS Reporting.