ESMTP

from The Free On-line Dictionary of Computing (8 July 2008)
ESMTP

   <messaging, protocol> Extended {SMTP}.  Initially defined in
   {RFC 1869} and extended thereafter.

   See also {ETRN}.

   (1997-11-21)
from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)
ESMTP
       Extended Simple Message Transport Protocol (SMTP, RFC 1425/1869)
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