A Registry for SMTP Enhanced Mail System Status Codes
RFC 5248

Network Working Group                                          T. Hansen
Request for Comments: 5248                             AT&T Laboratories
BCP: 138                                                      J. Klensin
Updates: 3463, 4468, 4954                                      June 2008
Category: Best Current Practice

         A Registry for SMTP Enhanced Mail System Status Codes

Status of This Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Abstract

   The specification for enhanced mail system status codes, RFC 3463,
   establishes a new code model and lists a collection of status codes.
   While it anticipated that more codes would be added over time, it did
   not provide an explicit mechanism for registering and tracking those
   codes.  This document specifies an IANA registry for mail system
   enhanced status codes, and initializes that registry with the codes
   so far established in published standards-track documents, as well as
   other codes that have become established in the industry.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 2
     2.1.  SMTP Enhanced Status Codes Registry . . . . . . . . . . . . 2
     2.2.  Review Process for New Values . . . . . . . . . . . . . . . 4
     2.3.  Registration Updates  . . . . . . . . . . . . . . . . . . . 4
     2.4.  Initial Values  . . . . . . . . . . . . . . . . . . . . . . 5
   3.  Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 9
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 9
     5.1.  Normative References  . . . . . . . . . . . . . . . . . . . 9
     5.2.  Informative References  . . . . . . . . . . . . . . . . . . 9

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RFC 5248           SMTP Enhanced Status Code Registry          June 2008

1.  Introduction

   Enhanced Status Codes for SMTP were first defined in [RFC1893], which
   was subsequently replaced by [RFC3463].  While it anticipated that
   more codes would be added over time (see section 2 of [RFC3463]), it
   did not provide an explicit mechanism for registering and tracking
   those codes.  Since then, various RFCs have been published and
   internet drafts proposed that define additional status codes.
   However, without an IANA registry, conflicts in definitions have
   begun to appear.

   This RFC defines such an IANA registry and was written to help
   prevent further conflicts from appearing in the future.  It
   initializes the registry with the established standards-track
   enhanced status codes from [RFC3463], [RFC3886], [RFC4468], and
   [RFC4954].  In addition, this document adds several codes to the
   registry that were established by various internet drafts and have
   come into common use, despite the expiration of the documents
   themselves.

   As specified in [RFC3463], an enhanced status code consists of a
   three-part code, with each part being numeric and separated by a
   period character.  The three portions are known as the class sub-
   code, the subject sub-code, and the detail sub-code.  In the tables,
   a wildcard for the class sub-code is represented by an X, a wildcard
   for a subject sub-code is represented by an XXX, and a wildcard for a
   detail sub-code is represented by a YYY.  For example, 3.XXX.YYY has
   an unspecified subject sub-code and an unspecified status code, and
   X.5.0 is has an unspecified class sub-code.  (This is a change from
   [RFC3463], which uses XXX for both the subject sub-code and detail
   sub-code wildcards.)

2.  IANA Considerations

2.1.  SMTP Enhanced Status Codes Registry

   IANA has created the registry "SMTP Enhanced Status Codes".  The SMTP
   Enhanced Status Codes registry will have three tables:

   o  Class Sub-Codes
      Each of the entries in this table represent class sub-codes and
      all have an unspecified subject sub-code and an unspecified detail
      sub-code.

   o  Subject Sub-Codes
      Each of the entries in this table represent subject sub-codes and
      all have an unspecified class sub-code and an unspecified detail
      sub-code.

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RFC 5248           SMTP Enhanced Status Code Registry          June 2008

   o  Enumerated Status Codes
      Each of the entries in this table represent the combination of a
      subject sub-code and a detail sub-code.  All entries will have an