Internet Message Access Protocol version 4 - LIST Command Extensions
RFC 5258

Network Working Group                                           B. Leiba
Request for Comments: 5258               IBM T.J. Watson Research Center
Obsoletes: 3348                                              A. Melnikov
Updates: 2193                                              Isode Limited
Category: Standards Track                                      June 2008

  Internet Message Access Protocol version 4 - LIST Command Extensions

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.

Abstract

   IMAP4 has two commands for listing mailboxes: LIST and LSUB.  As we
   have added extensions, such as Mailbox Referrals, that have required
   specialized lists we have had to expand the number of list commands,
   since each extension must add its function to both LIST and LSUB, and
   these commands are not, as they are defined, extensible.  If we've
   needed the extensions to work together, we've had to add a set of
   commands to mix the different options, the set increasing in size
   with each new extension.  This document describes an extension to the
   base LIST command that will allow these additions to be done with
   mutually compatible options to the LIST command, avoiding the
   exponential increase in specialized list commands.

Leiba & Melnikov            Standards Track                     [Page 1]
RFC 5258             IMAP4 LIST Command Extensions             June 2008

Table of Contents

   1.  Introduction and Overview  . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  4
   3.  Extended LIST Command  . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Initial List of Selection Options  . . . . . . . . . . . .  7
     3.2.  Initial List of Return Options . . . . . . . . . . . . . .  8
     3.3.  General Principles for Returning LIST Responses  . . . . .  9
     3.4.  Additional Requirements on LIST-EXTENDED Clients . . . . .  9
     3.5.  CHILDINFO Extended Data Item . . . . . . . . . . . . . . . 10
   4.  The CHILDREN Return Option . . . . . . . . . . . . . . . . . . 11
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   6.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . . 19
   7.  Internationalization Considerations  . . . . . . . . . . . . . 22
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23
     9.1.  Guidelines for IANA  . . . . . . . . . . . . . . . . . . . 23
     9.2.  Registration Procedure and Change Control  . . . . . . . . 23
     9.3.  Registration Template for LIST-EXTENDED Options  . . . . . 25
     9.4.  Initial LIST-EXTENDED Option Registrations . . . . . . . . 25
     9.5.  Registration Template for LIST-EXTENDED Extended Data
           Item . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
     9.6.  Initial LIST-EXTENDED Extended Data Item Registrations . . 28
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 29
     11.2. Informative References . . . . . . . . . . . . . . . . . . 30

Leiba & Melnikov            Standards Track                     [Page 2]
RFC 5258             IMAP4 LIST Command Extensions             June 2008

1.  Introduction and Overview

   The LIST command is extended by amending the syntax to allow options
   and multiple patterns to be specified.  The list of options replaces
   the several commands that are currently used to mix and match the
   information requested.  The new syntax is backward compatible, with
   no ambiguity: the new syntax is being used if one of the following
   conditions is true:

   1.  if the first word after the command name begins with a
       parenthesis ("LIST selection options")

   2.  if the second word after the command name begins with a
       parenthesis ("multiple mailbox patterns")

   3.  if the LIST command has more than 2 parameters ("LIST return
       options")

   Otherwise the original syntax is used.

   By adding options to the LIST command, we are announcing the intent
   to phase out and eventually to deprecate the RLIST and RLSUB commands
   described in [MBRef].  We are also defining the mechanism to request
   extended mailbox information, such as is described in the Child