draft-ietf-imapext-i18n-01.txt   draft-ietf-imapext-i18n-02.txt 
Network Working Group C. Newman Network Working Group Chris Newman
Internet-Draft Sun Microsystems Request for Comments: DRAFT Sun Microsystems
Expires: October 30, 2003 May 2003 draft-ietf-imapext-i18n-02.txt Arnt Gulbrandsen
Oryx Mail Systems
May 2004
Internet Message Access Protocol Internationalization Internet Message Access Protocol Internationalization
draft-ietf-imapext-i18n-01.txt
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society 2004. All Rights Reserved.
Abstract Abstract
Internet Message Access Protocol (IMAP) version 4rev1 has basic Internet Message Access Protocol (IMAP) version 4rev1 has basic
support for non-ASCII characters in mailbox names and search support for non-ASCII characters in mailbox names and search
substrings. It also supports non-ASCII message headers and content substrings. It also supports non-ASCII message headers and content
encoded as specified by Multipurpose Internet Mail Extensions (MIME). encoded as specified by Multipurpose Internet Mail Extensions
This specification defines a collection of IMAP extensions which (MIME). This specification defines a collection of IMAP extensions
improve international support including comparator negotiation for which improve international support including comparator negotiation
search, sort and thread, language negotiation for international error for search, sort and thread, language negotiation for international
text, and translations for namespace prefixes. error text, and translations for namespace prefixes.
Internet-draft May 2004
Table of Contents Table of Contents
1. Conventions Used in this Document . . . . . . . . . . . . . . 3 1. Conventions Used in this Document . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. LANGUAGE Extension . . . . . . . . . . . . . . . . . . . . . . 3 3. LANGUAGE Extension . . . . . . . . . . . . . . . . . . . . . 3
3.1 LANGUAGE Extension Requirements . . . . . . . . . . . . . . . 3 3.1 LANGUAGE Extension Requirements . . . . . . . . . . . . . . . 3
3.2 LANGUAGE Command . . . . . . . . . . . . . . . . . . . . . . . 4 3.2 LANGUAGE Command . . . . . . . . . . . . . . . . . . . . . . 4
3.3 LANGUAGE Response . . . . . . . . . . . . . . . . . . . . . . 6 3.3 LANGUAGE Response . . . . . . . . . . . . . . . . . . . . . . 5
3.4 TRANSLATION Extension to the NAMESPACE Response . . . . . . . 6 3.4 TRANSLATION Extension to the NAMESPACE Response . . . . . . . 6
3.5 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 7 3.5 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 6
4. COMPARATOR Extension . . . . . . . . . . . . . . . . . . . . . 7 4. COMPARATOR Extension . . . . . . . . . . . . . . . . . . . . 7
4.1 COMPARATOR Extension Requirements . . . . . . . . . . . . . . 8 4.1 COMPARATOR Extension Requirements . . . . . . . . . . . . . . 8
4.2 Comparators and Charsets . . . . . . . . . . . . . . . . . . . 9 4.2 Comparators and Charsets . . . . . . . . . . . . . . . . . . 9
4.3 COMPARATOR Command . . . . . . . . . . . . . . . . . . . . . . 9 4.3 COMPARATOR Command . . . . . . . . . . . . . . . . . . . . . 9
4.4 COMPARATOR Response . . . . . . . . . . . . . . . . . . . . . 10 4.4 COMPARATOR Response . . . . . . . . . . . . . . . . . . . . . 10
4.5 COMPARATOR SEARCH and SORT Key . . . . . . . . . . . . . . . . 10 4.5 COMPARATOR SEARCH and SORT Key . . . . . . . . . . . . . . . 10
4.6 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 11 4.6 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Other IMAP Internationalization Issues . . . . . . . . . . . . 11 5. Other IMAP Internationalization Issues . . . . . . . . . . . 11
5.1 UTF-8 Userids and Passwords . . . . . . . . . . . . . . . . . 11 5.1 UTF-8 Userids and Passwords . . . . . . . . . . . . . . . . . 11
5.2 UTF-8 Mailbox Names . . . . . . . . . . . . . . . . . . . . . 12 5.2 UTF-8 Mailbox Names . . . . . . . . . . . . . . . . . . . . . 12
5.3 UTF-8 Domains, Addresses and Mail Headers . . . . . . . . . . 12 5.3 UTF-8 Domains, Addresses and Mail Headers . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
9. Relevant Standards for i18n IMAP Implementations . . . . . . . 14 9. Relevant Standards for i18n IMAP Implementations . . . . . . 13
Normative References . . . . . . . . . . . . . . . . . . . . . 14 Normative References . . . . . . . . . . . . . . . . . . . . 14
Informative References . . . . . . . . . . . . . . . . . . . . 15 Informative References . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 15 Author's Address . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . 16 Intellectual Property and Copyright Statements . . . . . . . 16
1. Conventions Used in this Document Conventions Used in This Document
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
in this document are to be interpreted as defined in "Key words for in this document are to be interpreted as defined in "Key words for
use in RFCs to Indicate Requirement Levels" [1]. use in RFCs to Indicate Requirement Levels" [1].
The formal syntax use the Augmented Backus-Naur Form (ABNF) [2] The formal syntax use the Augmented Backus-Naur Form (ABNF) [2]
notation including the core rules defined in Appendix A of RFC 2234. notation including the core rules defined in Appendix A of RFC 2234.
In examples, "C:" and "S:" indicate lines sent by the client and In examples, "C:" and "S:" indicate lines sent by the client and
server respectively. If a single "C:" or "S:" label applies to server respectively. If a single "C:" or "S:" label applies to
multiple lines, then the line breaks between those lines are for multiple lines, then the line breaks between those lines are for
editorial clarity only and are not part of the actual protocol editorial clarity only and are not part of the actual protocol
exchange. exchange.
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2. Introduction 2. Introduction
This specification defines two IMAP4rev1 [6] extensions to enhance This specification defines two IMAP4rev1 [6] extensions to enhance
international support. These extensions can be advertised and international support. These extensions can be advertised and
implemented separately. implemented separately.
The LANGUAGE extension allows the client to request a suitable The LANGUAGE extension allows the client to request a suitable
language for protocol error messages and in combination with the language for protocol error messages and in combination with the
NAMESPACE extension [4] enables namespace translations. NAMESPACE extension [4] enables namespace translations.
The COMPARATOR extension allows the client to request a suitable The COMPARATOR extension allows the client to request a suitable
comparator which will modify the behavior of the base specification's comparator which will modify the behavior of the base
SEARCH command as well as the SORT and THREAD extensions [15]. This specification's SEARCH command as well as the SORT and THREAD
leverages the comparator registry [8]. extensions [15]. This leverages the comparator registry [8].
3. LANGUAGE Extension 3. LANGUAGE Extension
IMAP allows server responses to include human-readable text that in IMAP allows server responses to include human-readable text that in
many cases needs to be presented to the user. But that text is 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 limited to US-ASCII by the IMAP specification [6] in order to
preserve backwards compatibility with deployed IMAP implementations. preserve backwards compatibility with deployed IMAP implementations.
This section specifies a way for an IMAP client to negotiate which This section specifies a way for an IMAP client to negotiate which
language the server should use when sending human-readable text. language the server should use when sending human-readable text.
skipping to change at page 4, line 7 skipping to change at page 3, line 43
Assigning localized language aliases to shared mailboxes would be Assigning localized language aliases to shared mailboxes would be
done with a separate mechanism such as the proposed ANNOTATEMORE done with a separate mechanism such as the proposed ANNOTATEMORE
extension. [16] extension. [16]
3.1 LANGUAGE Extension Requirements 3.1 LANGUAGE Extension Requirements
IMAP servers that support this extension MUST list the keyword IMAP servers that support this extension MUST list the keyword
LANGUAGE in their CAPABILITY response as well as in the greeting LANGUAGE in their CAPABILITY response as well as in the greeting
CAPABILITY data. CAPABILITY data.
A server that advertises this extension MUST use the language A server that advertises this extension MUST use the language "i-
"i-default" as described in [3] as its default language until another default" as described in [3] as its default language until another
supported language is negotiated by the client. A server MUST include supported language is negotiated by the client. A server MUST
"i-default" as one of its supported languages. include "i-default" as one of its supported languages.
A client that supports this extension MUST be prepared for a possible A client that supports this extension MUST be prepared for a
NAMESPACE response [4] from the server. possible NAMESPACE response [4] from the server.
The LANGUAGE command is valid in not-authenticated, authenticated and The LANGUAGE command is valid in not-authenticated, authenticated
selected states. and selected states.
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3.2 LANGUAGE Command 3.2 LANGUAGE Command
Arguments: Optional language range argument. Arguments: Optional language range argument.
Response: A possible LANGUAGE response (see Section 3.3).
Response: A possible LANGUAGE response (see Section 3.3).
A possible NAMESPACE response as defined by [4]. A possible NAMESPACE response as defined by [4].
Result: OK - Command completed Result: OK - Command completed
NO - Could not complete command NO - Could not complete command
BAD - arguments invalid BAD - arguments invalid
The LANGUAGE command requests that human-readable text emitted by the The LANGUAGE command requests that human-readable text emitted by
server be localized to the language matching the language range the server be localized to a language matching the language range
argument as described by section 2.5 of RFC 3066. argument as described by section 2.5 of RFC 3066.
If the command succeeds, the server will return human-readable If the command succeeds, the server will return human-readable
responses in the specified language starting with the tagged OK responses in the specified language starting with the tagged OK
response to the LANGUAGE command. These responses will be in UTF-8 response to the LANGUAGE command. These responses will be in UTF-8
[7]. [7].
If the command fails, the server will continue to return If the command fails, the server will continue to return human-
human-readable responses in the language it was previously using. readable responses in the language it was previously using.
The client MUST NOT use MUL (Multiple languages) or UND The client MUST NOT use MUL (Multiple languages) or UND
(Undetermined) language tags and the server MUST return BAD if either (Undetermined) language tags and the server MUST return BAD if
tag is used. The special "*" language range argument indicates a either tag is used. The special "*" language range argument
request to use a language designated as preferred by the server indicates a request to use a language designated as preferred by the
administrator. The preferred language MAY vary based on the server administrator. The preferred language MAY vary based on the
currently active user. currently active user.
If the language range does not match a known language tag exactly but If the language range does not match a known language tag exactly
does match a language by the rules of section 2.5 of [5], the server but does match a language by the rules of section 2.5 of [5], the
MUST send an untagged LANGUAGE response indicating the language server MUST send an untagged LANGUAGE response indicating the
selected. language selected.
If the language range argument is omitted, the server SHOULD send an If the language range argument is omitted, the server SHOULD send an
untagged LANGUAGE response listing the languages it supports. If the untagged LANGUAGE response listing the languages it supports. If
server is unable to enumerate the list of languages it supports it the server is unable to enumerate the list of languages it supports
MAY return a tagged NO response to the enumeration request. it MAY return a tagged NO response to the enumeration request.
< The server defaults to using English i-default responses until < The server defaults to using English i-default responses until
the user explicitly changes the language. > the user explicitly changes the language. >
C: A001 LOGIN KAREN PASSWORD C: A001 LOGIN KAREN PASSWORD
S: A001 OK LOGIN completed S: A001 OK LOGIN completed
< Client requested MUL language. Server MUST reply with BAD > < Client requested MUL language. Server MUST reply with BAD. >
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C: A002 LANGUAGE MUL C: A002 LANGUAGE MUL
S: A002 BAD Invalid language MUL S: A002 BAD Invalid language MUL
< A LANGUAGE command with no arguments is a request to enumerate < A LANGUAGE command with no arguments is a request to enumerate
the list of languages the server supports. > the list of languages the server supports. >
C: A003 LANGUAGE C: A003 LANGUAGE
S: * LANGUAGE (EN DE IT i-default) S: * LANGUAGE (EN DE IT i-default)
S: A003 OK Supported languages have been enumerated S: A003 OK Supported languages have been enumerated
skipping to change at page 5, line 46 skipping to change at page 5, line 35
S: A004 OK La Language commande a ete execute avec success S: A004 OK La Language commande a ete execute avec success
< If a server does not support the requested primary language, < If a server does not support the requested primary language,
responses will continue to be returned in the current language responses will continue to be returned in the current language
the server is using. > the server is using. >
C: A005 LANGUAGE DE C: A005 LANGUAGE DE
S: A005 NO Ce Language n'est pas supporte S: A005 NO Ce Language n'est pas supporte
C: A006 LANGUAGE FR-CA C: A006 LANGUAGE FR-CA
S: * LANGUAGE (FR) S: * LANGUAGE (FR-CA)
S: A006 OK La Language commande a ete execute avec success S: A006 OK La Language commande a ete execute avec success
C: A007 LANGUAGE "*" C: A007 LANGUAGE "*"
S: * LANGUAGE (FR) S: * LANGUAGE (FR)
S: A007 OK La Language commande a ete execute avec success S: A007 OK La Language commande a ete execute avec success
3.3 LANGUAGE Response 3.3 LANGUAGE Response
Contents: A list of one or more language tags. Contents: A list of one or more language tags.
The LANGUAGE response occurs as a result of a LANGUAGE command. A The LANGUAGE response occurs as a result of a LANGUAGE command. A
LANGUAGE response with a list containing a single language tag LANGUAGE response with a list containing a single language tag
skipping to change at page 6, line 16 skipping to change at page 6, line 5
Contents: A list of one or more language tags. Contents: A list of one or more language tags.
The LANGUAGE response occurs as a result of a LANGUAGE command. A The LANGUAGE response occurs as a result of a LANGUAGE command. A
LANGUAGE response with a list containing a single language tag LANGUAGE response with a list containing a single language tag
indicates that the server is now using that language. A LANGUAGE indicates that the server is now using that language. A LANGUAGE
response with a list containing multiple language tags indicates the response with a list containing multiple language tags indicates the
server is communicating a list of available languages to the client, server is communicating a list of available languages to the client,
and no change in the active language has been made. and no change in the active language has been made.
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3.4 TRANSLATION Extension to the NAMESPACE Response 3.4 TRANSLATION Extension to the NAMESPACE Response
If the server supports the IMAP4 NAMESPACE command [4], the server If the server supports the IMAP4 NAMESPACE command [4], the server
MUST return an untagged NAMESPACE response when a language is MUST return an untagged NAMESPACE response when a language is
negotiated. However the server MUST NOT return a NAMESPACE response negotiated. However the server MUST NOT return a NAMESPACE response
if it is in not-authenticated state. if it is in not-authenticated state.
If as a result of the newly negotiated language, localized If as a result of the newly negotiated language, localized
representations of the namespace prefixes are available, the server representations of the namespace prefixes are available, the server
SHOULD include these in the TRANSLATION extension to the NAMESPACE SHOULD include these in the TRANSLATION extension to the NAMESPACE
response. response.
The TRANSLATION extension to the NAMESPACE response returns a single The TRANSLATION extension to the NAMESPACE response returns a single
string, containing the modified UTF-7 [6] encoded translation of the string, containing the modified UTF-7 [6] encoded translation of the
namespace prefix. It is the responsibility of the client to convert namespace prefix. It is the responsibility of the client to convert
between the namespace prefix and the translation of the namespace between the namespace prefix and the translation of the namespace
prefix when presenting mailbox names to the user. prefix when presenting mailbox names to the user.
In this example a server supports the IMAP4 NAMESPACE command. It In this example a server supports the IMAP4 NAMESPACE command. It
uses no prefix to the user's Personal Namespace, a prefix of "Other 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" Users" to its Other Users' Namespace and a prefix of "Public
to its only Shared Namespace. Since a client will often display Folders" to its only Shared Namespace. Since a client will often
these prefixes to the user, the server includes a translation of them display these prefixes to the user, the server includes a
that can be presented to the user. translation of them that can be presented to the user.
C: A001 LANGUAGE FR-CA C: A001 LANGUAGE FR-CA
S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION" S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION"
("Autres Utilisateurs/"))) (("Public Folders/" "/" ("Autres Utilisateurs/"))) (("Public Folders/" "/"
"TRANSLATION" ("R&Aok-pertoires Publics/"))) "TRANSLATION" ("R&Aok-pertoires Publics/")))
S: A001 OK La Language commande a ete executee avec success S: A001 OK La Language commande a ete executee avec success
3.5 Formal Syntax 3.5 Formal Syntax
The following syntax specification inherits ABNF [2] rules from The following syntax specification inherits ABNF [2] rules from
IMAP4rev1 [6], IMAP4 Namespace [4], Tags for the Identification of IMAP4rev1 [6], IMAP4 Namespace [4], Tags for the Identification of
Languages [5], and UTF-8 [7]. Languages [5], and UTF-8 [7].
command-any =/ language-cmd command-any =/ language-cmd
; LANGUAGE command is valid in all states ; LANGUAGE command is valid in all states
mailbox-data =/ language-data
language-cmd = "LANGUAGE" [SP lang-range-quoted] language-cmd = "LANGUAGE" [SP lang-range-quoted]
language-data = "LANGUAGE" SP "(" language-data = "LANGUAGE" SP "(" lang-tag-quoted *(SP lang-
lang-tag-quoted *(SP lang-tag-quoted) ")" tag-quoted) ")"
namespace-trans = SP DQUOTE "TRANSLATION" DQUOTE SP "(" string
")"
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namespace-trans = SP DQUOTE "TRANSLATION" DQUOTE SP "(" string ")"
; the string is encoded in Modified UTF-7. ; the string is encoded in Modified UTF-7.
; this is a subset of the syntax permitted by ; this is a subset of the syntax permitted by
; the Namespace_Response_Extension rule in RFC 2342 ; the Namespace_Response_Extension rule in RFC 2342
lang-range-quoted = astring lang-range-quoted = astring
; Once any literal wrapper or quoting is removed, this follows ; Once any literal wrapper or quoting is removed, this
; the language-range rule in section 2.5 of RFC 3066 ; follows the language-range rule in section 2.5 of RFC 3066
lang-tag-quoted = astring lang-tag-quoted = astring
; Once any literal wrapper or quoting is removed, this follows ; Once any literal wrapper or quoting is removed, this
follows
; the Language-Tag rule in section 2.1 of RFC 3066 ; the Language-Tag rule in section 2.1 of RFC 3066
; After the server is changed to a language other than i-default, ; After the server is changed to a language other than
; the resp-text rule from RFC 3501 is replaced with the following: ; i-default, the resp-text rule from RFC 3501 is replaced
; with the following:
resp-text = ["[" resp-text-code "]" SP ] resp-text = ["[" resp-text-code "]" SP ] UTF8-TEXT-CHAR
UTF8-TEXT-CHAR *(UTF8-TEXT-CHAR / "[") *(UTF8-TEXT-CHAR / "[")
UTF8-TEXT-CHAR = %x20-%x5A / %x5C-%x7E / UTF8-2 / UTF8-3 / UTF8-4 UTF8-TEXT-CHAR = %x20-%x5A / %x5C-%x7E / UTF8-2 / UTF8-3 /
UTF8-4
; UTF-8 excluding 7-bit control characters and "[" ; UTF-8 excluding 7-bit control characters and "["
4. COMPARATOR Extension 4. COMPARATOR Extension
IMAP4rev1 [6] includes the SEARCH command which can be used to locate IMAP4rev1 [6] includes the SEARCH command which can be used to
messages matching criteria including human-readable text. The SORT locate messages matching criteria including human-readable text.
extension [15] to IMAP allows the client to ask the server to The SORT extension [15] to IMAP allows the client to ask the server
determine the order of messages based on criteria including to determine the order of messages based on criteria including
human-readable text. These mechanisms require the ability to support human-readable text. These mechanisms require the ability to
non-English search and sort functions. support non-English search and sort functions.
This section defines an IMAP extension to negotiate use of This section defines an IMAP extension to negotiate use of
comparators [8] to internationalize IMAP SEARCH, SORT and THREAD. comparators [8] to internationalize IMAP SEARCH, SORT and THREAD.
The IMAP extension consists of a new command to determine or change The IMAP extension consists of a new command to determine or change
the active comparator, a new response to indicate the active the active comparator, a new response to indicate the active
comparator and possibly other available comparators, SEARCH and SORT comparator and possibly other available comparators, SEARCH and SORT
keys which can be used to change comparators on-the-fly, and an 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 additional response code to indicate that the failure of a SEARCH or
SORT command was due to an invalid comparator. SORT command was due to an invalid comparator.
The term "default comparator" refers to the comparator which is used The term "default comparator" refers to the comparator which is used
by SEARCH and SORT absent any negotiation using the COMPARATOR by SEARCH and SORT absent any negotiation using the COMPARATOR
command or SEARCH/SORT key. The term "active comparator" refers to command or SEARCH/SORT key. The term "active comparator" refers to
the comparator which will be used within a session by SEARCH and SORT the comparator which will be used within a session by SEARCH and
absent use of the COMPARATOR SEARCH/SORT key. The COMPARATOR command SORT absent use of the COMPARATOR SEARCH/SORT key. The COMPARATOR
is used to change the active comparator. The term "selected
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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" refers to the comparator selected by the most recent
COMPARATOR SEARCH/SORT key within the context of the current SEARCH/ COMPARATOR SEARCH/SORT key within the context of the current SEARCH/
SORT program or the active comparator if there is no COMPARATOR SORT program or the active comparator if there is no COMPARATOR
SEARCH/SORT key yet seen in context. SEARCH/SORT key yet seen in context.
The selected comparator applies to the following SEARCH keys: "BCC", The selected comparator applies to the following SEARCH keys: "BCC",
"BODY", "CC", "FROM", "SUBJECT", "TEXT", "TO" and "HEADER". If the "BODY", "CC", "FROM", "SUBJECT", "TEXT", "TO" and "HEADER". If the
server also advertises the "SORT" extension, then the selected server also advertises the "SORT" extension, then the selected
comparator applies to the following SORT keys: "CC", "FROM", comparator applies to the following SORT keys: "CC", "FROM",
"SUBJECT" and "TO". If the server advertises the "SUBJECT" and "TO". If the server advertises the
THREAD=ORDEREDSUBJECT, then the active comparator applies to the THREAD=ORDEREDSUBJECT, then the active comparator applies to the
ORDEREDSUBJECT threading algorithm. ORDEREDSUBJECT threading algorithm.
For SORT and THREAD, the pre-processing necessary to extract the base For SORT and THREAD, the pre-processing necessary to extract the
subject text from a Subject header occurs prior to the application of base subject text from a Subject header occurs prior to the
a comparator. application of a comparator.
4.1 COMPARATOR Extension Requirements 4.1 COMPARATOR Extension Requirements
IMAP servers that support this extension MUST list the keyword IMAP servers that support this extension MUST list the keyword
COMPARATOR in their CAPABILITY data once IMAP enters authenticated COMPARATOR in their CAPABILITY data once IMAP enters authenticated
state. state.
A server that advertises this extension MUST implement the A server that advertises this extension MUST implement the en;ascii-
en;ascii-casemap and i;octet comparators. A server intended to be casemap and i;octet comparators, as defined in [8]. A server
deployed globally MUST implement the i;basic-uca=3.1.1-uv=3.2 intended to be deployed globally MUST implement the
comparator. i;basic;uca=3.1.1;uv=3.2 comparator.
A server that advertises this extension MUST use a registered A server that advertises this extension MUST use a registered case-
case-insensitive comparator which supports the substring matching insensitive comparator which supports the substring matching
function as the default comparator. If the server also advertises function as the default comparator. If the server also advertises
the SORT or THREAD=ORDEREDSUBJECT extensions, then the default the SORT or THREAD=ORDEREDSUBJECT extensions, then the default
comparator MUST also support the ordering function. The selection of comparator MUST also support the ordering function. The selection
the default comparator MAY be adjustable by the server administrator, of the default comparator MAY be adjustable by the server
and MAY be sensitive to the current user. Once the IMAP connection administrator, and MAY be sensitive to the current user. Once the
enters authenticated state, the default comparator MUST remain static IMAP connection enters authenticated state, the default comparator
for the remainder of that connection. MUST remain static for the remainder of that connection.
A server that advertises this extension MUST support UTF-8 as a A server that advertises this extension MUST support UTF-8 as a
SEARCH charset. SEARCH charset.
The COMPARATOR command is valid in authenticated and selected states. The COMPARATOR command is valid in authenticated and selected
states.
Internet-draft May 2004
4.2 Comparators and Charsets 4.2 Comparators and Charsets
For SEARCH, SORT and THREAD operations that apply to message headers, For SEARCH, SORT and THREAD operations that apply to message
the server is responsible for removing the MIME header encoding [10] headers, the server is responsible for removing the MIME header
and converting the text of any known charsets to UTF-8 prior to encoding [10] and converting the text of any known charsets to UTF-8
applying the comparator algorithm. Unknown charsets should never prior to applying the comparator algorithm. Unknown charsets should
match when using the SEARCH command, and will sort together with never match when using the SEARCH command, and will sort together
invalid comparator input for the SORT and THREAD commands. with invalid comparator input for the SORT and THREAD commands.
When message text is in a known charset other than UTF-8, the server 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 is responsible for converting that text to UTF-8 prior to applying
the comparator. When message text is in an unknown charset, then the the comparator. When message text is in an unknown charset, then
text should be skipped by the SEARCH command unless the comparator is the text should be skipped by the SEARCH command unless the
i;octet. comparator is i;octet.
4.3 COMPARATOR Command 4.3 COMPARATOR Command
Arguments: Optional comparator order arguments. Arguments: Optional comparator order arguments.
Response: A possible COMPARATOR response (see Section 4.4). Response: A possible COMPARATOR response (see Section 4.4).
Result: OK - Command completed Result: OK - Command completed
NO - No matching comparator found NO - No matching comparator found
BAD - arguments invalid BAD - arguments invalid
The COMPARATOR command is used to determine or change the active The COMPARATOR command is used to determine or change the active
comparator. When issued with no arguments, it will result in a comparator. When issued with no arguments, it will result in a
COMPARATOR response indicating the currently active comparator. When COMPARATOR response indicating the currently active comparator.
issued with one or more comparator order argument, it will change the When issued with one or more comparator order argument, it will
active comparator if any comparator matches any argument. The change the active comparator if any comparator matches any argument.
COMPARATOR response will list other matching comparators if more than The COMPARATOR response will list other matching comparators if more
one matches the specified patterns. than one matches the specified patterns.
When the single argument "*" is used with the COMPARATOR command, it When the single argument "*" is used with the COMPARATOR command, it
will set the active comparator to be the default comparator. will activate the server's default comparator.
< The client requests activating a Czech comparator if possible,
or else a generic international comparator which it considers
suitable for Czech. The server picks the 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 4.4 COMPARATOR Response
Contents: The active comparator. Contents: The active comparator.
An optional list of available matching comparators An optional list of available matching comparators
The COMPARATOR response occurs as a result of a COMPARATOR command. The COMPARATOR response occurs as a result of a COMPARATOR command.
The first argument in the comparator response is the name of the The first argument in the comparator response is the name of the
active comparator. The second argument is a list of comparators active comparator. The second argument is a list of comparators
which matched any of the arguments to the COMPARATOR command and is which matched any of the arguments to the COMPARATOR command and is
present only if more than one match is found. present only if more than one match is found.
4.5 COMPARATOR SEARCH and SORT Key 4.5 COMPARATOR SEARCH and SORT Key
[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 The COMPARATOR SEARCH key takes a comparator order argument. That
argument will select the comparator to use for subsequent SEARCH keys argument will select the comparator to use for subsequent SEARCH
in the search program. The COMPARATOR SORT key works in a similar keys in the search specification. The COMPARATOR SORT key works in
fashion except that it applies to subsequent SORT keys in the SORT a similar fashion except that it applies to subsequent SORT keys in
criterion. the SORT criterion.
If no comparator matches the pattern specified by the COMPARATOR If no comparator matches the pattern specified by the COMPARATOR
SEARCH or SORT key, then the SEARCH or SORT command will fail with a 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 [BADCOMPARATOR] response code. This error code is also returned if
comparator is found, but it does not support the necessary function a comparator is found, but it does not support the necessary
(substring matching for SEARCH, or ordering for SORT). function (substring matching for SEARCH, or ordering for SORT).
If an input string provided as part of a SEARCH program causes an If an input string provided as part of a SEARCH program causes an
error when used with the selected comparator, the SEARCH command will error when used with the selected comparator, the SEARCH command
fail with a [BADMATCH] response code. will fail with a [BADMATCH] response code.
4.6 Formal Syntax 4.6 Formal Syntax
The following syntax specification inherits ABNF [2] rules from The following syntax specification inherits ABNF [2] rules from
IMAP4rev1 [6], and Internet Application Protocol Comparator Registry IMAP4rev1 [6], and Internet Application Protocol Comparator Registry
[8]. [8].
command-auth =/ comparator-cmd command-auth =/ comparator-cmd
mailbox-data =/ comparator-data
search-key =/ comparator-key search-key =/ comparator-key
Internet-draft May 2004
sort-criterion =/ comparator-key sort-criterion =/ comparator-key
; this only applies to servers which advertise both ; this only applies to servers which advertise both
; the COMPARATOR and SORT extensions. ; the COMPARATOR and SORT extensions.
resp-text-code =/ "BADCOMPARATOR" / "BADMATCH" resp-text-code =/ "BADCOMPARATOR" / "BADMATCH"
comparator-cmd = "COMPARATOR" *(SP comp-order-quoted) comparator-cmd = "COMPARATOR" *(SP comp-order-quoted)
comparator-data = "COMPARATOR" SP comp-sel-quoted [SP "(" comparator-data = "COMPARATOR" SP comp-sel-quoted [SP "("
comp-name-quoted *(SP comp-name-quoted) ")"] comp-name-quoted *(SP comp-name-quoted) ")"]
skipping to change at page 11, line 51 skipping to change at page 11, line 41
5. Other IMAP Internationalization Issues 5. Other IMAP Internationalization Issues
The following sections provide an overview of various other IMAP The following sections provide an overview of various other IMAP
internationalization issues. These issues are not resolved by this internationalization issues. These issues are not resolved by this
specification, but could be resolved by future standards work. specification, but could be resolved by future standards work.
5.1 UTF-8 Userids and Passwords 5.1 UTF-8 Userids and Passwords
IMAP4rev1 presently restricts the userid and password fields of the IMAP4rev1 presently restricts the userid and password fields of the
LOGIN command to US-ASCII. Because the ability to enter a userid and LOGIN command to US-ASCII. Because the ability to enter a userid
password is necessary to use IMAP at all for most authentication and password is necessary to use IMAP at all for most authentication
mechanisms, the potential lack of input methods for non-ASCII text is mechanisms, the potential lack of input methods for non-ASCII text
a serious interoperability concern. However, because of the is a serious interoperability concern. However, because of the
visibility of these fields to end-users, it is expected that pressure visibility of these fields to end-users, it is expected that
to support UTF-8 login names and passwords will eventually become pressure to support UTF-8 login names and passwords will eventually
irresistable. This specification defers such work until the become irresistable. This specification defers such work until the
SASL-related profile of stringprep [12] is published as an RFC, and SASL-related profile of stringprep [12] is published as an RFC, and
the impact on ACLs and email addresses has been assessed. the impact on ACLs and email addresses has been assessed.
The "userid" and "password" fields of the IMAP LOGIN command are The "userid" and "password" fields of the IMAP LOGIN command are
restricted to US-ASCII only until a future standards track RFC states restricted to US-ASCII only until a future standards track RFC
otherwise. Servers are encouraged to validate both fields to make
sure they conform to the formal syntax of UTF-8 and to reject the Internet-draft May 2004
LOGIN command if that syntax is violated. Servers MAY reject the use
of any 8-bit in the "userid" or "password" field. 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 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 described in section
modified UTF-7 mailbox naming convention was a mistake and we should 5.1.3 of RFC 3501 is best viewed as an transition from the status
have used UTF-8 instead. However, the preliminary design discussions quo in 1996 when modified UTF-7 was first specified. At that time,
to create a transitional mechanism for UTF-8 mailbox names suggests there was widespread unofficial use of local character sets such as
that the cost of supporting both a UTF-8 mechanism and a modified ISO-8859-1 and Shift-JIS for non-ASCII mailbox names, with resultant
UTF-7 convention for mailbox names during a transition period might non-interoperability.
exceed the benefit of the eventual goal. Because of this
controversy, UTF-8 mailbox name mechanisms are not included in this
specification.
The requirements in section 5.1 of RFC 3501 are very important if 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. 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 5.3 UTF-8 Domains, Addresses and Mail Headers
There is now an IETF standard for Internationalizing Domain Names in There is now an IETF standard for Internationalizing Domain Names in
Applications [13]. While IMAP clients are free to support this Applications [13]. While IMAP clients are free to support this
standard and convert punycode [14] to UTF-8 at display time, an 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 argument can be made that it would be helpful to simple clients if
the IMAP server could perform this conversion (the same argument the IMAP server could perform this conversion (the same argument
would apply to MIME header encoding [10]). However, it would be would apply to MIME header encoding [10]). However, it would be
unwise to move forward with such work until the work in progress to unwise to move forward with such work until the work in progress to
define the format of international email addresses is complete. define the format of international email addresses is complete.
6. IANA Considerations 6. IANA Considerations
When this is published as an RFC, the following IMAP extensions will When this is published as an RFC, the IMAP extensions LANGUAGE and
be registered: COMPARATOR are registered.
+-----------------+------------+
| Capability Name | Reference |
+-----------------+------------+
| LANGUAGE | [RFC XXXX] |
| COMPARATOR | [RFC XXXX] |
+-----------------+------------+
7. Security Considerations 7. Security Considerations
The LANGUAGE extension makes a new command available in "Not The LANGUAGE extension makes a new command available in "Not
Authenticated" state in IMAP. Some IMAP implementations run with Authenticated" state in IMAP. Some IMAP implementations run with
root privilege when the server is in "Not Authenticated" state and do root privilege when the server is in "Not Authenticated" state and
not revoke that privilege until after authentication is complete. do not revoke that privilege until after authentication is complete.
Such implementations are particularly vulnerable to buffer overflow Such implementations are particularly vulnerable to buffer overflow
security errors at this stage and need to implement parsing of this security errors at this stage and need to implement parsing of this
command with extra care. command with extra care.
Internet-draft May 2004
A LANGUAGE command issued prior to activation of a security layer is A LANGUAGE command issued prior to activation of a security layer is
subject to an active attack which suppresses or modifies the subject to an active attack which suppresses or modifies the
negotiation and thus makes STARTTLS or authentication error messages negotiation and thus makes STARTTLS or authentication error messages
more difficult to interpret. This is not a new attack as the error more difficult to interpret. This is not a new attack as the error
messages themselves are subject to active attack. Clients MUST messages themselves are subject to active attack. Clients MUST re-
re-issue the LANGUAGE command once a security layer is active, so issue the LANGUAGE command once a security layer is active, so this
this does not impact subsequent protocol operations. does not impact subsequent protocol operations.
Both the LANGUAGE and COMPARATOR extensions use the UTF-8 charset, Both the LANGUAGE and COMPARATOR extensions use the UTF-8 charset,
thus the security considerations for UTF-8 [7] are relevent. thus the security considerations for UTF-8 [7] are relevent.
However, neither uses UTF-8 for identifiers so the most serious However, neither uses UTF-8 for identifiers so the most serious
concerns do not apply. concerns do not apply.
8. Acknowledgements 8. Acknowledgements
The LANGUAGE extension is based on a previous Internet draft by Mike The LANGUAGE extension is based on a previous Internet draft by Mike
Gahrns and Alexey Melnikov, a substantial portion of the text in that Gahrns and Alexey Melnikov, a substantial portion of the text in
section was written by them. Many people have participated in that section was written by them. Many people have participated in
discussions about an IMAP Language extension in the various fora of discussions about an IMAP Language extension in the various fora of
the IETF and Internet working groups, so any list of contributors is the IETF and Internet working groups, so any list of contributors is
bound to be incomplete. However, the authors would like to thank bound to be incomplete. However, the authors would like to thank
Andrew McCown for early work on the original proposal, John Myers for Andrew McCown for early work on the original proposal, John Myers
suggestions regarding the namespace issue, along with Jutta Degener, for suggestions regarding the namespace issue, along with Jutta
Mark Crispin, Mark Pustilnik and Larry Osterman for their many Degener, Mark Crispin, Mark Pustilnik and Larry Osterman for their
suggestions that have been incorporated into this document. many suggestions that have been incorporated into this document.
Initial discussion of the COMPARATOR extension involved input from Initial discussion of the COMPARATOR extension involved input from
Mark Crispin and other participants of the IMAP Extensions WG. Mark Crispin and other participants of the IMAP Extensions WG.
9. Relevant Standards for i18n IMAP Implementations 9. Relevant Standards for i18n IMAP Implementations
This is a non-normative list of standards to consider when This is a non-normative list of standards to consider when
implementing i18n aware IMAP software. implementing i18n aware IMAP software.
o The LANGUAGE and COMPARATOR extensions to IMAP (this o The LANGUAGE and COMPARATOR extensions to IMAP (this
specification). specification).
o The 8-bit rules for mailbox naming in section 5.1 of RFC 3501. 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 o The Mailbox International Naming Convention in section 5.1.3 of
RFC 3501. RFC 3501.
o MIME [9] for message bodies. o MIME [9] for message bodies.
o MIME header encoding [10] for message headers. o MIME header encoding [10] for message headers.
o MIME Parameter Value and Encoded Word Extensions [11] for o MIME Parameter Value and Encoded Word Extensions [11] for
filenames. Quality IMAP server implementations will automatically filenames. Quality IMAP server implementations will
combine multipart parameters when generating the BODYSTRUCTURE. automatically combine multipart parameters when generating the
There is also some deployed non-standard use of MIME header BODYSTRUCTURE. There is also some deployed non-standard use of
encoding inside double-quotes for filenames. MIME header encoding inside double-quotes for filenames.
Internet-draft May 2004
o IDNA [13] and punycode [14] for domain names (presently only o IDNA [13] and punycode [14] for domain names (presently only
relevant to IMAP clients). relevant to IMAP clients).
o The UTF-8 charset [7]. o The UTF-8 charset [7].
o The IETF policy on Character Sets and Languages [3]. o The IETF policy on Character Sets and Languages [3].
Normative References Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Crocker, D. and P. Overell, "Augmented BNF for Syntax [2] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997. Specifications: ABNF", RFC 2234, November 1997.
[3] Alvestrand, H., "IETF Policy on Character Sets and Languages", [3] Alvestrand, H., "IETF Policy on Character Sets and Languages",
BCP 18, RFC 2277, January 1998. BCP 18, RFC 2277, January 1998.
[4] Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342, May 1998. [4] Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342, May
1998.
[5] Alvestrand, H., "Tags for the Identification of Languages", BCP [5] Alvestrand, H., "Tags for the Identification of Languages", BCP
47, RFC 3066, January 2001. 47, RFC 3066, January 2001.
[6] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", [6] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
RFC 3501, March 2003. 4rev1", RFC 3501, March 2003.
[7] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD [7] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD
63, RFC 3629, November 2003. 63, RFC 3629, November 2003.
[8] Newman, C., "Internet Application Protocol Comparator Registry", [8] Newman, C., "Internet Application Protocol Comparator
draft-newman-i18n-comparator-01 (work in progress), October Registry", draft-newman-i18n-comparator-01 (work in progress),
2003. October 2003. This draft has expired; a new draft will be
published by Ned Freed.
Informative References Informative References
[9] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [9] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies", Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996. RFC 2045, November 1996.
[10] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part [10] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part
Three: Message Header Extensions for Non-ASCII Text", RFC 2047, Three: Message Header Extensions for Non-ASCII Text", RFC 2047,
November 1996. November 1996.
[11] Freed, N. and K. Moore, "MIME Parameter Value and Encoded Word [11] Freed, N. and K. Moore, "MIME Parameter Value and Encoded Word
Extensions: Character Sets, Languages, and Continuations", RFC Extensions: Character Sets, Languages, and Continuations", RFC
2231, November 1997. 2231, November 1997.
Internet-draft May 2004
[12] Hoffman, P. and M. Blanchet, "Preparation of Internationalized [12] Hoffman, P. and M. Blanchet, "Preparation of Internationalized
Strings ("stringprep")", RFC 3454, December 2002. Strings ("stringprep")", RFC 3454, December 2002.
[13] Faltstrom, P., Hoffman, P. and A. Costello, "Internationalizing [13] Faltstrom, P., Hoffman, P. and A. Costello, "Internationalizing
Domain Names in Applications (IDNA)", RFC 3490, March 2003. Domain Names in Applications (IDNA)", RFC 3490, March 2003.
[14] Costello, A., "Punycode: A Bootstring encoding of Unicode for [14] Costello, A., "Punycode: A Bootstring encoding of Unicode for
Internationalized Domain Names in Applications (IDNA)", RFC Internationalized Domain Names in Applications (IDNA)", RFC
3492, March 2003. 3492, March 2003.
[15] Crispin, M. and K. Murchison, "INTERNET MESSAGE ACCESS PROTOCOL [15] Crispin, M. and K. Murchison, "INTERNET MESSAGE ACCESS PROTOCOL
- SORT AND THREAD EXTENSION", draft-ietf-imapext-sort-12 (work - SORT AND THREAD EXTENSION", draft-ietf-imapext-sort-12 (work
in progress), March 2003. in progress), March 2003.
[16] Daboo, C., "IMAP ANNOTATEMORE Extension", [16] Daboo, C., "IMAP ANNOTATEMORE Extension", draft-daboo-imap-
draft-daboo-imap-annotatemore-02 (work in progress), March annotatemore-05 (work in progress), April 2004.
2003.
Author's Address Authors' Addresses
Chris Newman Chris Newman
Sun Microsystems Sun Microsystems
1050 Lakes Drive 1050 Lakes Drive
West Covina, CA 91790 West Covina, CA 91790
US US
EMail: chris.newman@sun.com Email: chris.newman@sun.com
Arnt Gulbrandsen
Oryx Mail Systems GmbH
Joseph-Dollinger-Bogen 14
D-80807 Muenchen
Germany
Email: arnt@oryx.com
Phone: +49 89 32356-401
Fax: +49 89 32356-409
Internet-draft May 2004
Intellectual Property Statement Intellectual Property Statement
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Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2003). All Rights Reserved.
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and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
Internet-draft May 2004
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
 End of changes. 

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