Network Working Group                                          C.                                       Chris Newman
Request for Comments: DRAFT                             Sun Microsystems
Expires: October 30, 2003
draft-ietf-imapext-i18n-02.txt                          Arnt Gulbrandsen
                                                       Oryx Mail Systems
                                                                May 2003 2004

         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
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    Internet-Drafts are draft documents valid for a maximum of six
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    The list of current Internet-Drafts can be accessed at http://  The list of Internet-Draft Internet-
    Draft Shadow Directories can be accessed at

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

Copyright Notice

    Copyright (C) The Internet Society (2003). 2004.  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.

Internet-draft                                                  May 2004

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  5
    3.4 TRANSLATION Extension to the NAMESPACE Response . . . . . . .  6
    3.5 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .  7  6
    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 10
    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 12
    7.  Security Considerations . . . . . . . . . . . . . . . . . . . 13 12
    8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 13
    9.  Relevant Standards for i18n IMAP Implementations  . . . . . . . 14 13
        Normative References  . . . . . . . . . . . . . . . . . . . . . 14
        Informative References  . . . . . . . . . . . . . . . . . . . . 15 14
        Author's Address  . . . . . . . . . . . . . . . . . . . . . . . 15
        Intellectual Property and Copyright Statements  . . . . . . . . 16


Conventions Used in this 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

Internet-draft                                                  May 2004

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
    CAPABILITY data.

    A server that advertises this extension MUST use the language
   "i-default" "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.

Internet-draft                                                  May 2004

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 a 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 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 selected.

    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 BAD. >

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        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) (FR-CA)
        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.

Internet-draft                                                  May 2004

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) lang-
                          tag-quoted) ")"

        namespace-trans = SP DQUOTE "TRANSLATION" DQUOTE SP "(" string

Internet-draft                                                  May 2004

            ; 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
            ; 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
            ; the Language-Tag rule in section 2.1 of RFC 3066

        ; After the server is changed to a language other than i-default,
        ; 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 /
            ; 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

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    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 en;ascii-
    casemap and i;octet comparators. comparators, as defined in [8].  A server
    intended to be deployed globally MUST implement the i;basic-uca=3.1.1-uv=3.2
    i;basic;uca=3.1.1;uv=3.2 comparator.

    A server that advertises this extension MUST use a registered
   case-insensitive 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

Internet-draft                                                  May 2004

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 i;octet.

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 activate the active server's default comparator.

        < The client requests activating a Czech comparator to be if possible,
          or else a generic international comparator which it considers
          suitable for Czech. The server picks the default first supported
          comparator. >

        C: A001 COMPARATOR cz;* i;basic*
        S: * COMPARATOR i;basic;uca=3.1.1;uv=3.2
        S: A001 OK Will use i;basic;uca=3.1.1;uv=3.2 for collation

Internet-draft                                                  May 2004

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.


        [NOTE: Unless someone objects strongly and wishes to implement
        it, I will drop section 4.5. I have not been able to find a
        good, reasonable example for it, and I don't like its
        preprocessor-like approach, making "SEARCH <a> <b>" differ from
        "SEARCH <b> <a>" if one of <a> or <b> uses COMPARATOR. --Arnt]

    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. specification.  The COMPARATOR SORT key works in
    a similar fashion except that it applies to subsequent SORT keys in
    the SORT criterion.

    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

Internet-draft                                                  May 2004

        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

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    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

    The modified UTF-7 mailbox naming convention was a mistake and we should
   have used UTF-8 instead.  However, described in section
    5.1.3 of RFC 3501 is best viewed as an transition from the preliminary design discussions
   to create a transitional mechanism for UTF-8 mailbox names suggests status
    quo in 1996 when modified UTF-7 was first specified.  At that the cost time,
    there was widespread unofficial use of supporting both a UTF-8 mechanism local character sets such as
    ISO-8859-1 and a modified
   UTF-7 convention Shift-JIS for non-ASCII 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
   specification. names, with resultant

    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. Servers
    are encourated to enforce them.

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] |
                    | LANGUAGE and
    COMPARATOR      | [RFC XXXX] |
                    +-----------------+------------+ are registered.

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.

Internet-draft                                                  May 2004

    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 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.

Internet-draft                                                  May 2004

      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].

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

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

         4rev1", RFC 3501, March 2003.

    [7]  Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD
         63, RFC 3629, November 2003.

    [8]  Newman, C., "Internet Application Protocol Comparator
         Registry", draft-newman-i18n-comparator-01 (work in progress),
         October 2003. This draft has expired; a new draft will be
         published by Ned Freed.

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.

Internet-draft                                                  May 2004

    [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 draft-daboo-imap-
         annotatemore-05 (work in progress), March

Author's Address April 2004.

Authors' Addresses

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



    Arnt Gulbrandsen
    Oryx Mail Systems GmbH
    Joseph-Dollinger-Bogen 14
    D-80807 Muenchen


    Phone: +49 89 32356-401
    Fax: +49 89 32356-409

Internet-draft                                                  May 2004

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Internet-draft                                                  May 2004



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