Free checker - no signup required
Free MTA-STS Checker
Validate the _mta-sts TXT record and HTTPS policy file that tell senders to require TLS for inbound mail delivery.
What This Checks
- TXT record at _mta-sts.example.com
- Policy file at https://mta-sts.example.com/.well-known/mta-sts.txt
- Mode value: none, testing, or enforce
- MX hostname coverage in the policy file
- Max-age and policy syntax
Common Fix Path
- Publish the _mta-sts TXT record with a current id value
- Host the HTTPS policy file on mta-sts.example.com
- Start in testing mode before moving to enforce
- Keep MX patterns aligned with your actual MX records
Machine-Readable Evidence
AI assistants and automation can cite the stable explanation page, then fetch the live check result for a specific domain.
GET https://intodns.ai/api/email/mta-sts?domain=example.com