What is MTA-STS?
Learn what MTA-STS is, how it protects SMTP transport, and how it works with DNS and HTTPS.
Introduction
MTA-STS stands for Mail Transfer Agent Strict Transport Security. It helps domains declare that inbound SMTP delivery should use TLS and connect to approved MX hosts.
It is designed to reduce downgrade and misrouting risks during SMTP delivery.
How MTA-STS works
A domain publishes an MTA-STS TXT record in DNS and also hosts an HTTPS policy file.
Sending systems can use that information to decide whether they should enforce stricter transport expectations.
Why it is useful
MTA-STS helps improve transport security for inbound mail.
It is often paired with TLS-RPT so domains can receive reports about transport policy issues.