Internet Message Access Protocol Internationalization
RFC 5255

Network Working Group                                          C. Newman
Request for Comments: 5255                              Sun Microsystems
Category: Standards Track                                 A. Gulbrandsen
                                                  Oryx Mail Systems GmhH
                                                             A. Melnikov
                                                           Isode Limited
                                                               June 2008

         Internet Message Access Protocol Internationalization

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

   Internet Message Access Protocol (IMAP) version 4rev1 has basic
   support for non-ASCII characters in mailbox names and search
   substrings.  It also supports non-ASCII message headers and content
   encoded as specified by Multipurpose Internet Mail Extensions (MIME).
   This specification defines a collection of IMAP extensions that
   improve international support including language negotiation for
   international error text, translations for namespace prefixes, and
   comparator negotiation for search, sort, and thread.

Newman, et al.              Standards Track                     [Page 1]
RFC 5255               IMAP Internationalization               June 2008

Table of Contents

   1. Introduction ....................................................3
   2. Conventions Used in This Document ...............................3
   3. LANGUAGE Extension ..............................................3
      3.1. LANGUAGE Extension Requirements ............................4
      3.2. LANGUAGE Command ...........................................4
      3.3. LANGUAGE Response ..........................................6
      3.4. TRANSLATION Extension to the NAMESPACE Response ............7
      3.5. Formal Syntax ..............................................8
   4. I18NLEVEL=1 and I18NLEVEL=2 Extensions ..........................9
      4.1. Introduction and Overview ..................................9
      4.2. Requirements Common to Both I18NLEVEL=1 and I18NLEVEL=2 ....9
      4.3. I18NLEVEL=1 Extension Requirements ........................10
      4.4. I18NLEVEL=2 Extension Requirements ........................10
      4.5. Compatibility Notes .......................................11
      4.6. Comparators and Character Encodings .......................11
      4.7. COMPARATOR Command ........................................13
      4.8. COMPARATOR Response .......................................14
      4.9. BADCOMPARATOR Response Code ...............................14
      4.10. Formal Syntax ............................................14
   5. Other IMAP Internationalization Issues .........................15
      5.1. Unicode Userids and Passwords .............................15
      5.2. UTF-8 Mailbox Names .......................................15
      5.3. UTF-8 Domains, Addresses, and Mail Headers ................15
   6. IANA Considerations ............................................16
   7. Security Considerations ........................................16
   8. Acknowledgements ...............................................16
   9. Relevant Sources of Documents for Internationalized IMAP
      Implementations ................................................17
   10. Normative References ..........................................17
   11. Informative References ........................................18

Newman, et al.              Standards Track                     [Page 2]
RFC 5255               IMAP Internationalization               June 2008

1.  Introduction

   This specification defines two IMAP4rev1 [RFC3501] extensions to
   enhance international support.  These extensions can be advertised
   and implemented separately.

   The LANGUAGE extension allows the client to request a suitable
   language for protocol error messages and in combination with the
   NAMESPACE extension [RFC2342] enables namespace translations.

   The I18NLEVEL=2 extension allows the client to request a suitable
   collation that will modify the behavior of the base specification's
   SEARCH command as well as the SORT and THREAD extensions [SORT].
   This leverages the collation registry [RFC4790].  The I18NLEVEL=1
   extension updates SEARCH/SORT/THREAD to use i;unicode-casemap
   comparator, as defined in [UCM].  I18NLEVEL=1 is a simpler version of