mail transport agent

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)