Glossary
Mail transport
MTA (Mail Transfer Agent)
A server that relays a message toward its destination, talking SMTP to the next MTA. Most authentication checks happen at the receiving MTA.
Defined in RFC 5598 §2.3.
Where this appears
The lessons that use this term, and what each is for.
Email Authentication FundamentalsThe path a message takesName every system a message passes through, and say which of them you control.Advanced Email TrustWhat opportunistic TLS leaves openDescribe the downgrade an on-path attacker performs, and why the sender never notices.Advanced Email TrustThree pieces, three failure pointsName every component an MTA-STS deployment needs and what happens when each is missing.Advanced Email TrustReading a policy fileRead any published policy and say exactly which hosts it permits and for how long.Advanced Email TrustReading oneName the cause behind each failure type a report can carry.Advanced Email TrustForward-confirmed reverse DNSVerify that a sending host names itself consistently in three places, and fix it when it does not.Advanced Email TrustMonitoring the setDefine the checks that catch each of those failures before a receiver does.