What is MTA-STS?

A policy that forces encrypted (TLS) delivery of email to a domain.

MTA-STS combines a TXT record at _mta-sts with a policy file at https://mta-sts.domain/.well-known/mta-sts.txt. It prevents attackers from downgrading mail delivery to plaintext.

Related terms

• DMARC: A policy telling receivers what to do with mail that fails SPF and DKIM alignment.
• BIMI: Brand Indicators for Message Identification: shows a brand logo next to authenticated email.
• SSL/TLS certificate: A certificate that proves a site's identity and enables HTTPS encryption.