RFC 1893 (rfc1893) - Page 1 of 15


Enhanced Mail System Status Codes



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Network Working Group                                        G. Vaudreuil
Request for Comments: 1893                         Octel Network Services
Category: Standards Track                                    January 1996


                   Enhanced Mail System Status Codes

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.

1.   Overview

   There currently is not a standard mechanism for the reporting of mail
   system errors except for the limited set offered by SMTP and the
   system specific text descriptions sent in mail messages.  There is a
   pressing need for a rich machine readable status code for use in
   delivery status notifications [DSN].  This document proposes a new
   set of status codes for this purpose.

   SMTP [SMTP] error codes have historically been used for reporting
   mail system errors.  Because of limitations in the SMTP code design,
   these are not suitable for use in delivery status notifications.
   SMTP provides about 12 useful codes for delivery reports.  The
   majority of the codes are protocol specific response codes such as
   the 354 response to the SMTP data command.  Each of the 12 useful
   codes are each overloaded to indicate several error conditions each.
   SMTP suffers some scars from history, most notably the unfortunate
   damage to the reply code extension mechanism by uncontrolled use.
   This proposal facilitates future extensibility by requiring the
   client to interpret unknown error codes according to the theory of
   codes while requiring servers to register new response codes.

   The SMTP theory of reply codes partitioned in the number space such a
   manner that the remaining available codes will not provide the space
   needed.  The most critical example is the existence of only 5
   remaining codes for mail system errors.  The mail system
   classification includes both host and mailbox error conditions.  The
   remaining third digit space would be completely consumed as needed to
   indicate MIME and media conversion errors and security system errors.

   A revision to the SMTP theory of reply codes to better distribute the
   error conditions in the number space will necessarily be incompatible
   with SMTP.  Further, consumption of the remaining reply-code number



Vaudreuil                   Standards Track


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