from
The Free On-line Dictionary of Computing (8 July 2008)
Message Transfer Agent
Mail Transfer Agent
Mail Transport Agent
Message Transport Agent
<messaging> (MTA, Mail Transfer Agent) Any program responsible
for delivering {e-mail} messages. Upon receiving a message
from a {Mail User Agent} or another MTA, often by {SMTP} over
the {Internet}, it stores it temporarily locally and analyses
the recipients and delivers it to any local addressees and/or
forwards it to other remote MTAs ({routing}) for delivery to
remote recipients. In either case it may edit and/or add to
the message {headers}.
The most widely used MTA for {Unix} is {sendmail}, which
communicates using {SMTP}.
[Other OSes?]
{RFC 2821} (SMTP) expands MTA as "Mail Transfer Agent" though
this is less common. Alternatives with "Transport" are also
seen but less correct.
(2007-06-01)