Source : Free On-Line Dictionary of Computing

Local Mail Transfer Protocol
     
         (LMTP) A {protocol} designed as an
        alternative to {ESMTP} for cases where the mail receiver does
        not manage a queue.  LMTP is an {application level} {protocol}
        that runs on top of {TCP/IP}.  It was initially defined in
        {RFC 2033}, and uses (with a few changes) the syntax and
        semantics of {ESMTP}.  It should be used only by specific
        prior arrangement and configuration, and it must not be used
        on TCP {port} 25 (the {SMTP} port).
     
        (2002-03-09)