RFC 2920 (rfc2920) - Page 2 of 9

SMTP Service Extension for Command Pipelining

RFC 2920              SMTP for Command Pipelining         September 2000


    (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 until some intermediate point in the
          SMTP dialogue.  When this is done material read from the TCP
          connection and kept in process buffers can be lost.

    (2)   Flushing the TCP input buffer when an SMTP command fails. SMTP
          commands often fail but there is no reason to flush the TCP
          input buffer when this happens.  Nevertheless, some SMTP
          servers do this.

    (3)   Improper processing and promulgation of SMTP command failures.
          For example, some SMTP servers will refuse to accept a DATA
          command if the last RCPT TO command fails, paying no attention
          to the success or failure of prior RCPT TO command results.
          Other servers will accept a DATA command even when all
          previous RCPT TO commands have failed. Although it is possible
          to accommodate this sort of behavior in a client that employs
          command pipelining, it does complicate the construction of the
          client unnecessarily.

   This memo uses the mechanism described in [RFC-1869] to define an
   extension to the SMTP service whereby an SMTP server can declare that
   it is capable of handling pipelined commands. The SMTP client can
   then check for this declaration and use pipelining only when the
   server declares itself capable of handling it.

1.1.  Requirements Notation

   This document occasionally uses terms that appear in capital letters.
   When the terms "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
   appear capitalized, they are being used to indicate particular
   requirements of this specification. A discussion of the meanings of
   the terms "MUST", "SHOULD", and "MAY" appears in [RFC-1123]; the
   terms "MUST NOT" and "SHOULD NOT" are logical extensions of this
   usage.

2.  Framework for the Command Pipelining Extension

   The Command Pipelining extension is defined as follows:

    (1)   the name of the SMTP service extension is Pipelining;

    (2)   the EHLO keyword value associated with the extension is
          PIPELINING;




Freed                       Standards Track