RFC 1854 (rfc1854) - Page 1 of 7

SMTP Service Extension for Command Pipelining

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Network Working Group                                           N. Freed
Request For Comments: 1854                  Innosoft International, Inc.
Category: Standards Track                          A. Cargille, WG Chair
                                                            October 1995

                         SMTP Service Extension
                         for Command Pipelining

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.


   This memo defines an extension to the SMTP service whereby a server
   can indicate the extent of its ability to accept multiple commands in
   a single TCP send operation. Using a single TCP send operation for
   multiple commands can improve SMTP performance significantly.


   Although SMTP is widely and robustly deployed, certain extensions may
   nevertheless prove useful. In particular, many parts of the Internet
   make use of high latency network links.

   SMTP's intrinsic one command-one response structure is significantly
   penalized by high latency links, often to the point where the factors
   contributing to overall connection time are dominated by the time
   spent waiting for responses to individual commands (turnaround time).

   In the best of all worlds it would be possible to simply deploy SMTP
   client software that makes use of command pipelining: batching up
   multiple commands into single TCP send operations. Unfortunately, the
   original SMTP specification [1] did not explicitly state that SMTP
   servers must support this.  As a result a non-trivial number of
   Internet SMTP servers cannot adequately handle command pipelining.
   Flaws known to exist in deployed servers include:

 (1)   Connection handoff and buffer flushes in the middle of
       the SMTP dialogue.  Creation of server processes for
       incoming SMTP connections is a useful, obvious, and
       harmless implementation technique. However, some SMTP
       servers defer process forking and connection handoff

Freed & Cargille            Standards Track

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