Acronym for Mail Transport Agent
A program to send mail from one machine to another, usually using SMTP, but occasionaly something weird and obscure like UUCP.
SendMail, Postfix and Exim are MTAs. Another one that is very popular with ISPs is DanBernstein's Qmail, written with security in mind, for which there has been no exploit since at least March 1997.
- MDA (Mail Delivery Agent)
- MSA (Mail Submission Agent)
- MUA (Mail User Agent)
- MAA (Mail Access Agent).
It is generally a bad idea to mess with a live MTA. To make extensive changes or even migrate, you should deploy the new configuration in a test environment first. Only once you fully trust your new setup should you even dream about replacing the existing one.