Inbound TLS policy check

MTA-STS Checker

Check whether a domain publishes an MTA-STS TXT record and serves a valid HTTPS policy file. MTA-STS helps protect inbound mail delivery by requiring TLS for mail sent to your domain.

Domain

This checks _mta-sts.domain and https://mta-sts.domain/.well-known/mta-sts.txt.

Privacy note: this only sends the domain name to the lookup API. No email headers or message content are used.

What MTA-STS checks

MTA-STS is different from SPF, DKIM and DMARC. SPF, DKIM and DMARC are about sender authentication. MTA-STS is about securing inbound SMTP delivery to your mail servers with TLS.