Network Working Group                                          C. Newman
Internet-Draft                                          Sun Microsystems
Expires: November 7, October 30, 2003                                       May 9, 2003

         Internet Message Access Protocol Internationalization

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at http://

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on November 7, October 30, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.


   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 which
   improve international support including comparator negotiation for
   search, sort and thread, language negotiation for international error
   text, and translations for namespace prefixes.

Table of Contents

   1.  Conventions Used in this Document  . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  LANGUAGE Extension . . . . . . . . . . . . . . . . . . . . . .  3
   3.1 LANGUAGE Extension Requirements  . . . . . . . . . . . . . . .  3
   3.2 LANGUAGE Command . . . . . . . . . . . . . . . . . . . . . . .  4
   3.3 LANGUAGE Response  . . . . . . . . . . . . . . . . . . . . . .  6
   3.4 TRANSLATION Extension to the NAMESPACE Response  . . . . . . .  6
   3.5 Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  COMPARATOR Extension . . . . . . . . . . . . . . . . . . . . .  7
   4.1 COMPARATOR Extension Requirements  . . . . . . . . . . . . . .  8
   4.2 Comparators and Charsets . . . . . . . . . . . . . . . . . . .  9
   4.3 COMPARATOR Command . . . . . . . . . . . . . . . . . . . . . .  9
   4.4 COMPARATOR Response  . . . . . . . . . . . . . . . . . . . . . 10
   4.5 COMPARATOR SEARCH and SORT Key . . . . . . . . . . . . . . . . 10
   4.6 Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . . 11
   5.  Other IMAP Internationalization Issues . . . . . . . . . . . . 11
   5.1 UTF-8 Userids and Passwords  . . . . . . . . . . . . . . . . . 11
   5.2 UTF-8 Mailbox Names  . . . . . . . . . . . . . . . . . . . . . 12
   5.3 UTF-8 Domains, Addresses and Mail Headers  . . . . . . . . . . 12
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   9.  Relevant Standards for i18n IMAP Implementations . . . . . . . 14
   10. Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . . 14
       Normative References . . . . . . . . . . . . . . . . . . . . . 14
       Informative References . . . . . . . . . . . . . . . . . . . . 15
       Author's Address . . . . . . . . . . . . . . . . . . . . . . . 16 15
       Intellectual Property and Copyright Statements . . . . . . . . 17 16

1. Conventions Used in this Document

   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
   in this document are to be interpreted as defined in "Key words for
   use in RFCs to Indicate Requirement Levels" [1].

   The formal syntax use the Augmented Backus-Naur Form (ABNF) [2]
   notation including the core rules defined in Appendix A of RFC 2234.

   In examples, "C:" and "S:" indicate lines sent by the client and
   server respectively.  If a single "C:" or "S:" label applies to
   multiple lines, then the line breaks between those lines are for
   editorial clarity only and are not part of the actual protocol

2. Introduction

   This specification defines two IMAP4rev1 [6] 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 [4] enables namespace translations.

   The COMPARATOR extension allows the client to request a suitable
   comparator which will modify the behavior of the base specification's
   SEARCH command as well as the SORT and THREAD extensions [15].  This
   leverages the comparator registry [8].

3. LANGUAGE Extension

   IMAP allows server responses to include human-readable text that in
   many cases needs to be presented to the user.  But that text is
   limited to US-ASCII by the IMAP specification [6] in order to
   preserve backwards compatibility with deployed IMAP implementations.
   This section specifies a way for an IMAP client to negotiate which
   language the server should use when sending human-readable text.

   The LANGUAGE extension only provides a mechanism for altering fixed
   server strings such as response text and NAMESPACE folder names.
   Assigning localized language aliases to shared mailboxes would be
   done with a separate mechanism such as the proposed ANNOTATEMORE
   extension. [16]

3.1 LANGUAGE Extension Requirements

   IMAP servers that support this extension MUST list the keyword
   LANGUAGE in their CAPABILITY response as well as in the greeting

   A server that advertises this extension MUST use the language
   "i-default" as described in [3] as its default language until another
   supported language is negotiated by the client. A server MUST include
   "i-default" as one of its supported languages.

   A client that supports this extension MUST be prepared for a possible
   NAMESPACE response [4] from the server.

   The LANGUAGE command is valid in not-authenticated, authenticated and
   selected states.

3.2 LANGUAGE Command

   Arguments: Optional language range argument.
   Response:  A possible LANGUAGE response (see Section 3.3).

              A possible NAMESPACE response as defined by [4].
   Result:    OK - Command completed
              NO - Could not complete command
              BAD - arguments invalid

   The LANGUAGE command requests that human-readable text emitted by the
   server be localized to the language matching the language range
   argument as described by section 2.5 of RFC 3066.

   If the command succeeds, the server will return human-readable
   responses in the specified language starting with the tagged OK
   response to the LANGUAGE command.  These responses will be in UTF-8

   If the command fails, the server will continue to return
   human-readable responses in the language it was previously using.

   The client MUST NOT use MUL (Multiple languages) or UND
   (Undetermined) language tags and the server MUST return BAD if either
   tag is used.  The special "*" language range argument indicates a
   request to use a language designated as preferred by the server
   administrator.  The preferred language MAY vary based on the
   currently active user.

   If the language range does not match a known language tag exactly but
   does match a language by the rules of section 2.5 of [5], the server
   MUST send an untagged LANGUAGE response indicating the language

   If the language range argument is omitted, the server SHOULD send an
   untagged LANGUAGE response listing the languages it supports.  If the
   server is unable to enumerate the list of languages it supports it
   MAY return a tagged NO response to the enumeration request.

      < The server defaults to using English i-default responses until
      the user explicitly changes the language. >

      S: A001 OK LOGIN completed

      < Client requested MUL language. Server MUST reply with BAD >

      C: A002 LANGUAGE MUL
      S: A002 BAD Invalid language MUL

      < A LANGUAGE command with no arguments is a request to enumerate
      the list of languages the server supports. >

      C: A003 LANGUAGE
      S: * LANGUAGE (EN DE IT i-default)
      S: A003 OK Supported languages have been enumerated

      C: B001 LANGUAGE
      S: B001 NO Server is unable to enumerate supported languages

      < Once the client changes the language, all responses will be in
      that language starting with the tagged OK to the LANGUAGE
      command. >

      C: A004 LANGUAGE FR
      S: A004 OK La Language commande a ete execute avec success

      < If a server does not support the requested primary language,
      responses will continue to be returned in the current language
      the server is using. >

      C: A005 LANGUAGE DE
      S: A005 NO Ce Language n'est pas supporte

      C: A006 LANGUAGE FR-CA
      S: * LANGUAGE (FR)
      S: A006 OK La Language commande a ete execute avec success

      C: A007 LANGUAGE "*"
      S: * LANGUAGE (FR)
      S: A007 OK La Language commande a ete execute avec success

3.3 LANGUAGE Response

   Contents:  A list of one or more language tags.

   The LANGUAGE response occurs as a result of a LANGUAGE command.  A
   LANGUAGE response with a list containing a single language tag
   indicates that the server is now using that language.  A LANGUAGE
   response with a list containing multiple language tags indicates the
   server is communicating a list of available languages to the client,
   and no change in the active language has been made.

3.4 TRANSLATION Extension to the NAMESPACE Response

   If the server supports the IMAP4 NAMESPACE command [4], the server
   MUST return an untagged NAMESPACE response when a language is
   negotiated.  However the server MUST NOT return a NAMESPACE response
   if it is in not-authenticated state.

   If as a result of the newly negotiated language, localized
   representations of the namespace prefixes are available, the server
   SHOULD include these in the TRANSLATION extension to the NAMESPACE

   The TRANSLATION extension to the NAMESPACE response returns a single
   string, containing the modified UTF-7 [6] encoded translation of the
   namespace prefix.  It is the responsibility of the client to convert
   between the namespace prefix and the translation of the namespace
   prefix when presenting mailbox names to the user.

   In this example a server supports the IMAP4 NAMESPACE command. It
   uses no prefix to the user's Personal Namespace, a prefix of "Other
   Users" to its Other Users' Namespace and a prefix of "Public Folders"
   to its only Shared Namespace.  Since a client will often display
   these prefixes to the user, the server includes a translation of them
   that can be presented to the user.

      C: A001 LANGUAGE FR-CA
      S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION"
           ("Autres Utilisateurs/"))) (("Public Folders/" "/"
           "TRANSLATION" ("R&Aok-pertoires Publics/")))
      S: A001 OK La Language commande a ete executee avec success

3.5 Formal Syntax

   The following syntax specification inherits ABNF [2] rules from
   IMAP4rev1 [6], IMAP4 Namespace [4], Tags for the Identification of
   Languages [5], and UTF-8 [7].

      command-any     =/ language-cmd
         ; LANGUAGE command is valid in all states

      mailbox-data    =/ language-data

      language-cmd    = "LANGUAGE" [SP lang-range-quoted]

      language-data   = "LANGUAGE" SP "("
                        lang-tag-quoted *(SP lang-tag-quoted) ")"

      namespace-trans = SP DQUOTE "TRANSLATION" DQUOTE SP "(" string ")"
         ; the string is encoded in Modified UTF-7.
         ; this is a subset of the syntax permitted by
         ; the Namespace_Response_Extension rule in RFC 2342

      lang-range-quoted = astring
         ; Once any literal wrapper or quoting is removed, this follows
         ; the language-range rule in section 2.5 of RFC 3066

      lang-tag-quoted = astring
         ; Once any literal wrapper or quoting is removed, this follows
         ; the Language-Tag rule in section 2.1 of RFC 3066

      ; After the server is changed to a language other than i-default,
      ; the resp-text rule from RFC 3501 is replaced with the following:

      resp-text       = ["[" resp-text-code "]" SP ]
                        UTF8-TEXT-CHAR *(UTF8-TEXT-CHAR / "[")

      UTF8-TEXT-CHAR  = %x20-%x5A / %x5C-%x7E / UTF8-2 / UTF8-3 / UTF8-4
         ; UTF-8 excluding 7-bit control characters and "["

4. COMPARATOR Extension

   IMAP4rev1 [6] includes the SEARCH command which can be used to locate
   messages matching criteria including human-readable text.  The SORT
   extension [15] to IMAP allows the client to ask the server to
   determine the order of messages based on criteria including
   human-readable text.  These mechanisms require the ability to support
   non-English search and sort functions.

   This section defines an IMAP extension to negotiate use of
   comparators [8] to internationalize IMAP SEARCH, SORT and THREAD.
   The IMAP extension consists of a new command to determine or change
   the active comparator, a new response to indicate the active
   comparator and possibly other available comparators, SEARCH and SORT
   keys which can be used to change comparators on-the-fly, and an
   additional response code to indicate that the failure of a SEARCH or
   SORT command was due to an invalid comparator.

   The term "default comparator" refers to the comparator which is used
   by SEARCH and SORT absent any negotiation using the COMPARATOR
   command or SEARCH/SORT key.  The term "active comparator" refers to
   the comparator which will be used within a session by SEARCH and SORT
   absent use of the COMPARATOR SEARCH/SORT key.  The COMPARATOR command
   is used to change the active comparator.  The term "selected
   comparator" refers to the comparator selected by the most recent
   COMPARATOR SEARCH/SORT key within the context of the current SEARCH/
   SORT program or the active comparator if there is no COMPARATOR
   SEARCH/SORT key yet seen in context.

   The selected comparator applies to the following SEARCH keys: "BCC",
   "BODY", "CC", "FROM", "SUBJECT", "TEXT", "TO" and "HEADER".  If the
   server also advertises the "SORT" extension, then the selected
   comparator applies to the following SORT keys: "CC", "FROM",
   "SUBJECT" and "TO".  If the server advertises the
   THREAD=ORDEREDSUBJECT, then the active comparator applies to the
   ORDEREDSUBJECT threading algorithm.

   For SORT and THREAD, the pre-processing necessary to extract the base
   subject text from a Subject header occurs prior to the application of
   a comparator.

4.1 COMPARATOR Extension Requirements

   IMAP servers that support this extension MUST list the keyword
   COMPARATOR in their CAPABILITY data once IMAP enters authenticated

   A server that advertises this extension MUST implement the
   en;ascii-casemap and i;octet comparators.  A server intended to be
   deployed globally MUST implement the i;basic-uca=3.1.1-uv=3.2

   A server that advertises this extension MUST use a registered
   case-insensitive comparator which supports the substring matching
   function as the default comparator.  If the server also advertises
   the SORT or THREAD=ORDEREDSUBJECT extensions, then the default
   comparator MUST also support the ordering function.  The selection of
   the default comparator MAY be adjustable by the server administrator,
   and MAY be sensitive to the current user.  Once the IMAP connection
   enters authenticated state, the default comparator MUST remain static
   for the remainder of that connection.

   A server that advertises this extension MUST support UTF-8 as a
   SEARCH charset.

   The COMPARATOR command is valid in authenticated and selected states.

4.2 Comparators and Charsets

   For SEARCH, SORT and THREAD operations that apply to message headers,
   the server is responsible for removing the MIME header encoding [10]
   and converting the text of any known charsets to UTF-8 prior to
   applying the comparator algorithm.  Unknown charsets should never
   match when using the SEARCH command, and will sort together with
   invalid comparator input for the SORT and THREAD commands.

   When message text is in a known charset other than UTF-8, the server
   is responsible for converting that text to UTF-8 prior to applying
   the comparator.  When message text is in an unknown charset, then the
   text should be skipped by the SEARCH command unless the comparator is

4.3 COMPARATOR Command

   Arguments: Optional comparator order arguments.
   Response:  A possible COMPARATOR response (see Section 4.4).
   Result:    OK - Command completed
              NO - No matching comparator found
              BAD - arguments invalid

   The COMPARATOR command is used to determine or change the active
   comparator.  When issued with no arguments, it will result in a
   COMPARATOR response indicating the currently active comparator.  When
   issued with one or more comparator order argument, it will change the
   active comparator if any comparator matches any argument.  The
   COMPARATOR response will list other matching comparators if more than
   one matches the specified patterns.

   When the single argument "*" is used with the COMPARATOR command, it
   will set the active comparator to be the default comparator.

4.4 COMPARATOR Response

   Contents:  The active comparator.
              An optional list of available matching comparators

   The COMPARATOR response occurs as a result of a COMPARATOR command.
   The first argument in the comparator response is the name of the
   active comparator.  The second argument is a list of comparators
   which matched any of the arguments to the COMPARATOR command and is
   present only if more than one match is found.


   The COMPARATOR SEARCH key takes a comparator order argument.  That
   argument will select the comparator to use for subsequent SEARCH keys
   in the search program.  The COMPARATOR SORT key works in a similar
   fashion except that it applies to subsequent SORT keys in the SORT

   If no comparator matches the pattern specified by the COMPARATOR
   SEARCH or SORT key, then the SEARCH or SORT command will fail with a
   [BADCOMPARATOR] response code.  This error code is also returned if a
   comparator is found, but it does not support the necessary function
   (substring matching for SEARCH, or ordering for SORT).

   If an input string provided as part of a SEARCH program causes an
   error when used with the selected comparator, the SEARCH command will
   fail with a [BADMATCH] response code.

4.6 Formal Syntax

   The following syntax specification inherits ABNF [2] rules from
   IMAP4rev1 [6], and Internet Application Protocol Comparator Registry

      command-auth      =/ comparator-cmd

      mailbox-data      =/ comparator-data

      search-key        =/ comparator-key

      sort-criterion    =/ comparator-key
         ; this only applies to servers which advertise both
         ; the COMPARATOR and SORT extensions.

      resp-text-code    =/ "BADCOMPARATOR" / "BADMATCH"

      comparator-cmd    = "COMPARATOR" *(SP comp-order-quoted)

      comparator-data   = "COMPARATOR" SP comp-sel-quoted [SP "("
                           comp-name-quoted *(SP comp-name-quoted) ")"]

      comparator-key    = "COMPARATOR" SP comp-order-quoted

      comp-name-quoted  = astring
         ; Once any literal wrapper or quoting is removed,
         ; this follows the comparator-name rule

      comp-order-quoted = astring
         ; Once any literal wrapper or quoting is removed,
         ; this follows the comparator-order rule

      comp-sel-quoted   = astring
         ; Once any literal wrapper or quoting is removed,
         ; this follows the comparator-sel rule

5. Other IMAP Internationalization Issues

   The following sections provide an overview of various other IMAP
   internationalization issues.  These issues are not resolved by this
   specification, but could be resolved by future standards work.

5.1 UTF-8 Userids and Passwords

   IMAP4rev1 presently restricts the userid and password fields of the
   LOGIN command to US-ASCII.  Because the ability to enter a userid and
   password is necessary to use IMAP at all for most authentication
   mechanisms, the potential lack of input methods for non-ASCII text is
   a serious interoperability concern.  However, because of the
   visibility of these fields to end-users, it is expected that pressure
   to support UTF-8 login names and passwords will eventually become
   irresistable.  This specification defers such work until the
   SASL-related profile of stringprep [12] is published as an RFC, and
   the impact on ACLs and email addresses has been assessed.

   The "userid" and "password" fields of the IMAP LOGIN command are
   restricted to US-ASCII only until a future standards track RFC states
   otherwise.  Servers are encouraged to validate both fields to make
   sure they conform to the formal syntax of UTF-8 and to reject the
   LOGIN command if that syntax is violated.  Servers MAY reject the use
   of any 8-bit in the "userid" or "password" field.

5.2 UTF-8 Mailbox Names

   There appears to be rough concensus in the IMAP community that the
   modified UTF-7 mailbox naming convention was a mistake and we should
   have used UTF-8 instead.  However, the preliminary design discussions
   to create a transitional mechanism for UTF-8 mailbox names suggests
   that the cost of supporting both a UTF-8 mechanism and a modified
   UTF-7 convention for mailbox names during a transition period might
   exceed the benefit of the eventual goal.  Because of this
   controversy, UTF-8 mailbox name mechanisms are not included in this

   The requirements in section 5.1 of RFC 3501 are very important if
   we're ever going to be able to deploy UTF-8 mailbox names.

5.3 UTF-8 Domains, Addresses and Mail Headers

   There is now an IETF standard for Internationalizing Domain Names in
   Applications [13].  While IMAP clients are free to support this
   standard and convert punycode [14] to UTF-8 at display time, an
   argument can be made that it would be helpful to simple clients if
   the IMAP server could perform this conversion (the same argument
   would apply to MIME header encoding [10]).  However, it would be
   unwise to move forward with such work until the work in progress to
   define the format of international email addresses is complete.

6. IANA Considerations

   When this is published as an RFC, the following IMAP extensions will
   be registered:

                    | Capability Name | Reference  |
                    | LANGUAGE        | [RFC XXXX] |
                    | COMPARATOR      | [RFC XXXX] |

7. Security Considerations

   The LANGUAGE extension makes a new command available in "Not
   Authenticated" state in IMAP.  Some IMAP implementations run with
   root privilege when the server is in "Not Authenticated" state and do
   not revoke that privilege until after authentication is complete.
   Such implementations are particularly vulnerable to buffer overflow
   security errors at this stage and need to implement parsing of this
   command with extra care.

   A LANGUAGE command issued prior to activation of a security layer is
   subject to an active attack which suppresses or modifies the
   negotiation and thus makes STARTTLS or authentication error messages
   more difficult to interpret.  This is not a new attack as the error
   messages themselves are subject to active attack.  Clients MUST
   re-issue the LANGUAGE command once a security layer is active, so
   this does not impact subsequent protocol operations.

   Both the LANGUAGE and COMPARATOR extensions use the UTF-8 charset,
   thus the security considerations for UTF-8 [7] are relevent.
   However, neither uses UTF-8 for identifiers so the most serious
   concerns do not apply.

8. Acknowledgements

   The LANGUAGE extension is based on a previous Internet draft by Mike
   Gahrns and Alexey Melnikov, a substantial portion of the text in that
   section was written by them.  Many people have participated in
   discussions about an IMAP Language extension in the various fora of
   the IETF and Internet working groups, so any list of contributors is
   bound to be incomplete.  However, the authors would like to thank
   Andrew McCown for early work on the original proposal, John Myers for
   suggestions regarding the namespace issue, along with Jutta Degener,
   Mark Crispin, Mark Pustilnik and Larry Osterman for their many
   suggestions that have been incorporated into this document.

   Initial discussion of the COMPARATOR extension involved input from
   Mark Crispin and other participants of the IMAP Extensions WG.

9. Relevant Standards for i18n IMAP Implementations

   This is a non-normative list of standards to consider when
   implementing i18n aware IMAP software.
   o  The LANGUAGE and COMPARATOR extensions to IMAP (this
   o  The 8-bit rules for mailbox naming in section 5.1 of RFC 3501.
   o  The Mailbox International Naming Convention in section 5.1.3 of
      RFC 3501.
   o  MIME [9] for message bodies.
   o  MIME header encoding [10] for message headers.
   o  MIME Parameter Value and Encoded Word Extensions [11] for
      filenames.  Quality IMAP server implementations will automatically
      combine multipart parameters when generating the BODYSTRUCTURE.
      There is also some deployed non-standard use of MIME header
      encoding inside double-quotes for filenames.
   o  IDNA [13] and punycode [14] for domain names (presently only
      relevant to IMAP clients).
   o  The UTF-8 charset [7].
   o  The IETF policy on Character Sets and Languages [3].

10. Open Issues

   1.  Should there be an explicit request for the list of comparators
       in the COMPARATOR response code?

   2.  Should we add a command to fetch the lookup tables associated
       with a comparator?

   3.  Need examples for COMPARATOR extension.

Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 2234, November 1997.

   [3]  Alvestrand, H., "IETF Policy on Character Sets and Languages",
        BCP 18, RFC 2277, January 1998.

   [4]  Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342, May 1998.

   [5]  Alvestrand, H., "Tags for the Identification of Languages", BCP
        47, RFC 3066, January 2001.

        RFC 3501, March 2003.

   [7]  Yergeau, F., "UTF-8, a transformation format of ISO 10646",
        draft-yergeau-rfc2279bis-04 (work in progress), February STD
        63, RFC 3629, November 2003.

   [8]  Newman, C., "Internet Application Protocol Comparator Registry",
        draft-newman-i18n-comparator-01 (work in progress), May October

Informative References

   [9]   Freed, N. and N. Borenstein, "Multipurpose Internet Mail
         Extensions (MIME) Part One: Format of Internet Message Bodies",
         RFC 2045, November 1996.

   [10]  Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part
         Three: Message Header Extensions for Non-ASCII Text", RFC 2047,
         November 1996.

   [11]  Freed, N. and K. Moore, "MIME Parameter Value and Encoded Word
         Extensions: Character Sets, Languages, and Continuations", RFC
         2231, November 1997.

   [12]  Hoffman, P. and M. Blanchet, "Preparation of Internationalized
         Strings ("stringprep")", RFC 3454, December 2002.

   [13]  Faltstrom, P., Hoffman, P. and A. Costello, "Internationalizing
         Domain Names in Applications (IDNA)", RFC 3490, March 2003.

   [14]  Costello, A., "Punycode: A Bootstring encoding of Unicode for
         Internationalized Domain Names in Applications (IDNA)", RFC
         3492, March 2003.

   [15]  Crispin, M. and K. Murchison, "INTERNET MESSAGE ACCESS PROTOCOL
         - SORT AND THREAD EXTENSION", draft-ietf-imapext-sort-12 (work
         in progress), March 2003.

   [16]  Daboo, C., "IMAP ANNOTATEMORE Extension",
         draft-daboo-imap-annotatemore-02 (work in progress), March

Author's Address

   Chris Newman
   Sun Microsystems
   1050 Lakes Drive
   West Covina, CA  91790


Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights. Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11. Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard. Please address the information to the IETF Executive

Full Copyright Statement

   Copyright (C) The Internet Society (2003). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assignees.

   This document and the information contained herein is provided on an



   Funding for the RFC Editor function is currently provided by the
   Internet Society.