Question 1

What does an MTA-STS checker validate?

Accepted Answer

An MTA-STS checker verifies the DNS policy record and the HTTPS well-known policy file so you can confirm transport security settings are both published and reachable.

Question 2

Why do I need both the DNS record and the policy file?

Accepted Answer

Receivers need the DNS record to discover MTA-STS and the policy file to understand the actual mode and expected MX hosts. Missing either piece weakens the setup.

Question 3

When should teams run an MTA-STS lookup?

Accepted Answer

Run it after DNS or CDN changes, before enforcing transport expectations, and during mail-security reviews when SMTP TLS posture needs verification.

Question 4

What if the policy file is missing?

Accepted Answer

That usually means the HTTPS path is not published correctly, a CDN rule is stripping the response, or the file location is different from the expected .well-known path.

Free MTA-STS checker and policy lookup

Check the live MTA-STS record and policy file