Level: Advanced
Mail Transfer Agent Strict Transport Security lets a domain explicitly require encrypted, authenticated connections for mail sent to it, closing a gap that opportunistic TLS alone leaves open.
It Prevents Downgrade and Interception Attacks
Without MTA-STS, a connection can be forced down to unencrypted delivery through a man-in-the-middle attack; MTA-STS makes encryption a strict, published requirement rather than an optional negotiation.
It Requires Both a DNS Record and a Published Policy File
Implementing MTA-STS involves publishing a specific DNS TXT record alongside a policy file hosted at a defined, standardized URL on the domain, working together to declare the enforcement requirement.
It Protects Inbound Mail to Your Domain, Not Just Outbound
Unlike SPF, DKIM, and DMARC, which primarily concern authenticating your outbound mail, MTA-STS is specifically about protecting mail being delivered to your own domain.
Next step: Use the Find DNS Records to check whether your domain currently has an MTA-STS record published and correctly configured.