Glossary
MTA
Mail Transfer Agent: server software that moves messages between mail servers.
ValidReach Team · Updated 2026-10-26
In practice
It accepts a message over SMTP, finds the destination server through MX records and hands it on, retrying if the destination is busy. Well-known examples are Postfix and Exim.
Verification and sending
A mailbox check talks to the recipient’s MTA, which decides whether it would accept the address.