Contexts for IMAP4
RFC 5267

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• 05

Network Working Group                                        D. Cridland
Request for Comments: 5267                                       C. King
Category: Standards Track                                  Isode Limited
                                                               July 2008

                           Contexts for IMAP4

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 IMAP4rev1 protocol has powerful search facilities as part of the
   core protocol, but lacks the ability to create live, updated results
   that can be easily handled.  This memo provides such an extension,
   and shows how it can be used to provide a facility similar to virtual
   mailboxes.

Cridland & King             Standards Track                     [Page 1]
RFC 5267                      IMAP CONTEXT                     July 2008

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
   3.  Extended Sort Syntax . . . . . . . . . . . . . . . . . . . . .  3
     3.1.  ESORT Extension  . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Ranges in Extended Sort Results  . . . . . . . . . . . . .  4
     3.3.  Extended SORT Example  . . . . . . . . . . . . . . . . . .  4
   4.  Contexts . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  5
     4.2.  Context Hint . . . . . . . . . . . . . . . . . . . . . . .  5
     4.3.  Notifications of Changes . . . . . . . . . . . . . . . . .  6
       4.3.1.  Refusing to Update Contexts  . . . . . . . . . . . . .  7
       4.3.2.  Common Features of ADDTO and REMOVEFROM  . . . . . . .  8
       4.3.3.  ADDTO Return Data Item . . . . . . . . . . . . . . . .  8
       4.3.4.  REMOVEFROM Return Data Item  . . . . . . . . . . . . .  9
       4.3.5.  The CANCELUPDATE Command . . . . . . . . . . . . . . . 10
     4.4.  Partial Results  . . . . . . . . . . . . . . . . . . . . . 10
     4.5.  Caching Results  . . . . . . . . . . . . . . . . . . . . . 11
   5.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . . 12
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Appendix A.  Cookbook  . . . . . . . . . . . . . . . . . . . . . . 15
     A.1.  Virtual Mailboxes  . . . . . . . . . . . . . . . . . . . . 15
     A.2.  Trash Mailboxes  . . . . . . . . . . . . . . . . . . . . . 15
     A.3.  Immediate EXPUNGE Notifications  . . . . . . . . . . . . . 15
     A.4.  Monitoring Counts  . . . . . . . . . . . . . . . . . . . . 15
     A.5.  Resynchronizing Contexts . . . . . . . . . . . . . . . . . 16
   Appendix B.  Server Implementation Notes . . . . . . . . . . . . . 16

Cridland & King             Standards Track                     [Page 2]
RFC 5267                      IMAP CONTEXT                     July 2008

1.  Introduction

   Although the basic SEARCH command defined in [IMAP], and as enhanced
   by [ESEARCH], is relatively compact in its representation, this
   reduction saves only a certain amount of data, and huge mailboxes
   might overwhelm the storage available for results on even relatively
   high-end desktop machines.

   The SORT command defined in [SORT] provides useful features, but is
   hard to use effectively on changing mailboxes over low-bandwidth
   connections.

   This memo borrows concepts from [ACAP], such as providing a windowed
   view onto search or sort results, and making updates that are
   bandwidth and round-trip efficient.  These are provided by two
   extensions: "ESORT" and "CONTEXT".

2.  Conventions Used in This Document

   In examples, "C:" and "S:" indicate lines sent by the client
   messaging user agent and IMAP4rev1 ([IMAP]) server, respectively.
   "//" indicates inline comments not part of the protocol exchange.
   Line breaks are liberally inserted for clarity.  Examples are
   intended to be read in order, such that the state remains from one
   example to the next.

   Although the examples show a server that supports [ESEARCH], this is
   not a strict requirement of this specification.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this