The IMAP METADATA Extension
RFC 5464

Network Working Group                                           C. Daboo
Request for Comments: 5464                                   Apple, Inc.
Category: Standards Track                                  February 2009

                      The IMAP METADATA Extension

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

   The METADATA extension to the Internet Message Access Protocol
   permits clients and servers to maintain "annotations" or "metadata"
   on IMAP servers.  It is possible to have annotations on a per-mailbox
   basis or on the server as a whole.  For example, this would allow
   comments about the purpose of a particular mailbox to be "attached"
   to that mailbox, or a "message of the day" containing server status
   information to be made available to anyone logging in to the server.

Daboo                        Standards Track                    [Page 1]
RFC 5464               The IMAP METADATA Extension         February 2009

Table of Contents

   1.  Introduction and Overview  . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
   3.  Data Model . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Namespace of Entries . . . . . . . . . . . . . . . . . . .  4
       3.2.1.  Entry Names  . . . . . . . . . . . . . . . . . . . . .  5
     3.3.  Private versus Shared and Access Control . . . . . . . . .  6
   4.  IMAP Protocol Changes  . . . . . . . . . . . . . . . . . . . .  7
     4.1.  General Considerations . . . . . . . . . . . . . . . . . .  7
     4.2.  GETMETADATA Command  . . . . . . . . . . . . . . . . . . .  8
       4.2.1.  MAXSIZE GETMETADATA Command Option . . . . . . . . . .  9
       4.2.2.  DEPTH GETMETADATA Command Option . . . . . . . . . . . 10
     4.3.  SETMETADATA Command  . . . . . . . . . . . . . . . . . . . 10
     4.4.  METADATA Response  . . . . . . . . . . . . . . . . . . . . 12
       4.4.1.  METADATA Response with Values  . . . . . . . . . . . . 13
       4.4.2.  Unsolicited METADATA Response without Values . . . . . 13
   5.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . . 14
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
     6.1.  Entry and Attribute Registration Template  . . . . . . . . 16
     6.2.  Server Entry Registrations . . . . . . . . . . . . . . . . 16
       6.2.1.  /shared/comment  . . . . . . . . . . . . . . . . . . . 17
       6.2.2.  /shared/admin  . . . . . . . . . . . . . . . . . . . . 17
     6.3.  Mailbox Entry Registrations  . . . . . . . . . . . . . . . 17
       6.3.1.  /shared/comment  . . . . . . . . . . . . . . . . . . . 18
       6.3.2.  /private/comment . . . . . . . . . . . . . . . . . . . 18
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 19
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 19

Daboo                        Standards Track                    [Page 2]
RFC 5464               The IMAP METADATA Extension         February 2009

1.  Introduction and Overview

   The goal of the METADATA extension is to provide a means for clients
   to set and retrieve "annotations" or "metadata" on an IMAP server.
   The annotations can be associated with specific mailboxes or the
   server as a whole.  The server can choose to support only server
   annotations or both server and mailbox annotations.

   A server that supports both server and mailbox annotations indicates
   the presence of this extension by returning "METADATA" as one of the
   supported capabilities in the CAPABILITY command response.

   A server that supports only server annotations indicates the presence
   of this extension by returning "METADATA-SERVER" as one of the
   supported capabilities in the CAPABILITY command response.

   A server that supports unsolicited annotation change responses MUST
   support the "ENABLE" [RFC5161] extension to allow clients to turn
   that feature on.

   The METADATA extension adds two new commands and one new untagged
   response to the IMAP base protocol.

   This extension makes the following changes to the IMAP protocol:

   o  adds a new SETMETADATA command

   o  adds a new GETMETADATA command