(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).