draft-ietf-imapext-i18n-15.txt   rfc5255.txt 
Network Working Group Chris Newman Network Working Group C. Newman
Internet-Draft Sun Microsystems Request for Comments: 5255 Sun Microsystems
Intended Status: Proposed Standard Arnt Gulbrandsen Category: Standards Track A. Gulbrandsen
Oryx Mail Systems GmhH Oryx Mail Systems GmhH
Alexey Melnikov A. Melnikov
Isode Limited Isode Limited
February 1, 2008
Internet Message Access Protocol Internationalization Internet Message Access Protocol Internationalization
draft-ietf-imapext-i18n-15.txt
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Copyright (C) The IETF Trust (2008). This document specifies an Internet standards track protocol for the
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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 encoded as specified by Multipurpose Internet Mail Extensions (MIME).
(MIME). This specification defines a collection of IMAP extensions This specification defines a collection of IMAP extensions that
improve international support including language negotiation for
international error text, translations for namespace prefixes, and
comparator negotiation for search, sort, and thread.
Internet-draft February 2008 Table of Contents
which improve international support including comparator negotiation 1. Introduction ....................................................3
for search, sort and thread, language negotiation for international 2. Conventions Used in This Document ...............................3
error text, and translations for namespace prefixes. 3. LANGUAGE Extension ..............................................3
3.1. LANGUAGE Extension Requirements ............................4
3.2. LANGUAGE Command ...........................................4
3.3. LANGUAGE Response ..........................................6
3.4. TRANSLATION Extension to the NAMESPACE Response ............7
3.5. Formal Syntax ..............................................8
4. I18NLEVEL=1 and I18NLEVEL=2 Extensions ..........................9
4.1. Introduction and Overview ..................................9
4.2. Requirements Common to Both I18NLEVEL=1 and I18NLEVEL=2 ....9
4.3. I18NLEVEL=1 Extension Requirements ........................10
4.4. I18NLEVEL=2 Extension Requirements ........................10
4.5. Compatibility Notes .......................................11
4.6. Comparators and Character Encodings .......................11
4.7. COMPARATOR Command ........................................13
4.8. COMPARATOR Response .......................................14
4.9. BADCOMPARATOR Response Code ...............................14
4.10. Formal Syntax ............................................14
5. Other IMAP Internationalization Issues .........................15
5.1. Unicode Userids and Passwords .............................15
5.2. UTF-8 Mailbox Names .......................................15
5.3. UTF-8 Domains, Addresses, and Mail Headers ................15
6. IANA Considerations ............................................16
7. Security Considerations ........................................16
8. Acknowledgements ...............................................16
9. Relevant Sources of Documents for Internationalized IMAP
Implementations ................................................17
10. Normative References ..........................................17
11. Informative References ........................................18
Table of Contents 1. Introduction
1. Conventions Used in this Document . . . . . . . . . . . . . . 2 This specification defines two IMAP4rev1 [RFC3501] extensions to
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 enhance international support. These extensions can be advertised
3. LANGUAGE Extension . . . . . . . . . . . . . . . . . . . . . 3 and implemented separately.
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 . . . . . . . . . . . . . . . . . . . . . . . . 6
4. I18NLEVEL=1 and I18NLEVEL=2 Extensions . . . . . . . . . . . 7
4.1 Introduction and Overview . . . . . . . . . . . . . . . . . . 8
4.2 Requirements common to both I18NLEVEL=1 and I18NLEVEL=2 . . .
4.3 I18NLEVEL=1 Extension Requirements . . . . . . . . . . . . . 8
4.4 I18NLEVEL=2 Extension Requirements . . . . . . . . . . . . . 8
4.5 Compatibility Notes
4.6 Comparators and Charsets . . . . . . . . . . . . . . . . . . 9
4.7 COMPARATOR Command . . . . . . . . . . . . . . . . . . . . . 9
4.8 COMPARATOR Response . . . . . . . . . . . . . . . . . . . . . 10
4.9 BADCOMPARATOR Response Code . . . . . . . . . . . . . . . . .
4.10 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . 10
5. Other IMAP Internationalization Issues . . . . . . . . . . . 11
5.1 UTF-8 Userids and Passwords . . . . . . . . . . . . . . . . . 11
5.2 UTF-8 Mailbox Names . . . . . . . . . . . . . . . . . . . . . 11
5.3 UTF-8 Domains, Addresses and Mail Headers . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
9. Relevant Standards for i18n IMAP Implementations . . . . . . 13
Normative References . . . . . . . . . . . . . . . . . . . . 13
Informative References . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . 16
Conventions Used in This Document The LANGUAGE extension allows the client to request a suitable
language for protocol error messages and in combination with the
NAMESPACE extension [RFC2342] enables namespace translations.
The I18NLEVEL=2 extension allows the client to request a suitable
collation that will modify the behavior of the base specification's
SEARCH command as well as the SORT and THREAD extensions [SORT].
This leverages the collation registry [RFC4790]. The I18NLEVEL=1
extension updates SEARCH/SORT/THREAD to use i;unicode-casemap
comparator, as defined in [UCM]. I18NLEVEL=1 is a simpler version of
I18NLEVEL=2 with no ability to select a different collation.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
The formal syntax use the Augmented Backus-Naur Form (ABNF) The formal syntax uses the Augmented Backus-Naur Form (ABNF)
[RFC4234] notation including the core rules defined in Appendix A. [RFC5234] notation including the core rules defined in Appendix A.
Internet-draft February 2008
The UTF8-related productions are defined in [RFC3629]. The UTF-8-related productions are defined in [RFC3629].
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.
2. Introduction
This specification defines two IMAP4rev1 [RFC3501] extensions to
enhance international support. These extensions can be advertised
and implemented separately.
The LANGUAGE extension allows the client to request a suitable
language for protocol error messages and in combination with the
NAMESPACE extension [RFC2342] enables namespace translations.
The I18NLEVEL=2 extension allows the client to request a suitable
collation which will modify the behavior of the base specification's
SEARCH command as well as the SORT and THREAD extensions [SORT].
This leverages the collation registry [RFC4790].
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 [RFC3501] in order to limited to US-ASCII by the IMAP specification [RFC3501] 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.
The LANGUAGE extension only provides a mechanism for altering fixed The LANGUAGE extension only provides a mechanism for altering fixed
server strings such as response text and NAMESPACE folder names. server strings such as response text and NAMESPACE folder names.
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 METADATA done with a separate mechanism such as the proposed METADATA
extension (see [METADATA]). extension (see [METADATA]).
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 "i- A server that advertises this extension MUST use the language
"i-default" as described in [RFC2277] as its default language until
Internet-draft February 2008
default" as described in [RFC2277] as its default language until
another supported language is negotiated by the client. A server another supported language is negotiated by the client. A server
MUST include "i-default" as one of its supported languages. MUST include "i-default" as one of its supported languages. IMAP
servers SHOULD NOT advertise the LANGUAGE extension if they discover
that they only support "i-default".
Clients and servers that support this extension MUST also support Clients and servers that support this extension MUST also support the
the NAMESPACE extension [RFC2342]. NAMESPACE extension [RFC2342].
The LANGUAGE command is valid in all states. Clients are urged to The LANGUAGE command is valid in all states. Clients SHOULD issue
issue LANGUAGE before authentication, since some servers send LANGUAGE before authentication, since some servers send valuable user
valuable user information as part of authentication (e.g. "password information as part of authentication (e.g., "password is correct,
is correct, but expired"). If a security layer (such as SASL or but expired"). If a security layer (such as SASL or TLS) is
TLS) is subsequently negotiated by the client, it MUST re-issue the subsequently negotiated by the client, it MUST re-issue the LANGUAGE
LANGUAGE command in order to make sure that no previous active command in order to make sure that no previous active attack (if any)
attack (if any) on LANGUAGE negotiation has effect on subsequent on LANGUAGE negotiation has effect on subsequent error messages.
error messages. (See Section 7 for a more detailed explanation of (See Section 7 for a more detailed explanation of the attack.)
the attack.)
3.2 LANGUAGE Command 3.2. LANGUAGE Command
Arguments: Optional language range arguments. Arguments: Optional language range arguments.
Response: A possible LANGUAGE response (see section 3.3). Response: A possible LANGUAGE response (see Section 3.3).
A possible NAMESPACE response (see section 3.4). A possible NAMESPACE response (see Section 3.4).
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 LANGUAGE command requests that human-readable text emitted by the
the server be localized to a language matching one of the language server be localized to a language matching one of the language range
range argument as described by section 2 of [RFC4647]. argument as described by Section 2 of [RFC4647].
If the command succeeds, the server will return human-readable If the command succeeds, the server will return human-readable
responses in the first supported language specified. These responses in the first supported language specified. These responses
responses will be in UTF-8 [RFC3629]. The server MUST send a will be in UTF-8 [RFC3629]. The server MUST send a LANGUAGE response
LANGUAGE response specifying the language used, and the change takes specifying the language used, and the change takes effect immediately
effect immediately after the LANGUAGE response. after the LANGUAGE response.
If the command fails, the server continues to return human-readable If the command fails, the server continues to return human-readable
responses in the language it was previously using. responses in the language it was previously using.
The special "default" language range argument indicates a request to The special "default" language range argument indicates a request to
use a language designated as preferred by the server administrator. use a language designated as preferred by the server administrator.
The preferred language MAY vary based on the currently active user. The preferred language MAY vary based on the currently active user.
If a language range does not match a known language tag exactly but If a language range does not match a known language tag exactly but
does match a language by the rules of [RFC4647], the server MUST send
Internet-draft February 2008 an untagged LANGUAGE response indicating the language selected.
does match a language by the rules of [RFC4647], the server MUST
send an untagged LANGUAGE response indicating the language selected.
If there aren't any arguments, the server SHOULD send an untagged If there aren't any arguments, the server SHOULD send an untagged
LANGUAGE response listing the languages it supports. If the server LANGUAGE response listing the languages it supports. If the server
is unable to enumerate the list of languages it supports it MAY is unable to enumerate the list of languages it supports it MAY
return a tagged NO response to the enumeration request. return a tagged NO response to the enumeration request. If, after
receiving a LANGUAGE request, the server discovers that it doesn't
support any language other than i-default, it MUST 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, which no server supports. > < Client requested MUL language, which no server supports. >
C: A002 LANGUAGE MUL C: A002 LANGUAGE MUL
skipping to change at page 5, line 35 skipping to change at page 6, line 4
< 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
C: B001 LANGUAGE C: B001 LANGUAGE
S: B001 NO Server is unable to enumerate supported languages S: B001 NO Server is unable to enumerate supported languages
< Once the client changes the language, all responses will be in < Once the client changes the language, all responses will be in
that language starting after the LANGUAGE response. Note that that language starting after the LANGUAGE response. Note that
this includes the NAMESPACE response. Because RFCs are in US- this includes the NAMESPACE response. Because RFCs are in US-
ASCII, this document uses an ASCII transcription rather than ASCII, this document uses an ASCII transcription rather than
UTF-8 text, e.g. ue in the word "ausgefuehrt" > UTF-8 text, e.g., "ue" in the word "ausgefuehrt" >
C: C001 LANGUAGE DE C: C001 LANGUAGE DE
S: * LANGUAGE (DE) S: * LANGUAGE (DE)
S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION" S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION"
("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
"TRANSLATION" ("Gemeinsame Postf&AM8-cher/"))) "TRANSLATION" ("Gemeinsame Postf&AM8-cher/")))
S: C001 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt S: C001 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
< 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: D001 LANGUAGE FR C: D001 LANGUAGE FR
S: D001 NO Diese Sprache ist nicht unterstuetzt S: D001 NO Diese Sprache ist nicht unterstuetzt
Internet-draft February 2008
C: D002 LANGUAGE DE-IT C: D002 LANGUAGE DE-IT
S: * LANGUAGE (DE-IT) S: * LANGUAGE (DE-IT)
S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION" S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION"
("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
"TRANSLATION" ("Gemeinsame Postf&AM8-cher/"))) "TRANSLATION" ("Gemeinsame Postf&AM8-cher/")))
S: D002 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt S: D002 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
C: D003 LANGUAGE "default" C: D003 LANGUAGE "default"
S: * LANGUAGE (DE) S: * LANGUAGE (DE)
S: D003 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt S: D003 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
< Server does not speak French, but does speak English. User < Server does not speak French, but does speak English. User
speaks Canadian French and Canadian English. > speaks Canadian French and Canadian English. >
C: E001 LANGUAGE FR-CA EN-CA C: E001 LANGUAGE FR-CA EN-CA
S: * LANGUAGE (EN) S: * LANGUAGE (EN)
S: E001 OK Now speaking English S: E001 OK Now speaking English
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
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.
3.4 TRANSLATION Extension to the NAMESPACE Response 3.4. TRANSLATION Extension to the NAMESPACE Response
If localized representations of the namespace prefixes are available If localized representations of the namespace prefixes are available
in the selected language, the server SHOULD include these in the in the selected language, the server SHOULD include these in the
TRANSLATION extension to the NAMESPACE response. TRANSLATION extension to the NAMESPACE 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 [RFC3501] encoded translation string, containing the modified UTF-7 [RFC3501] encoded translation
of the namespace prefix. It is the responsibility of the client to of the namespace prefix. It is the responsibility of the client to
convert between the namespace prefix and the translation of the convert between the namespace prefix and the translation of the
namespace prefix when presenting mailbox names to the user. namespace 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 Users" to its Other Users' Namespace, and a prefix of "Public
Folders" to its only Shared Namespace. Since a client will often Folders" to its only Shared Namespace. Since a client will often
display these prefixes to the user, the server includes a display these prefixes to the user, the server includes a translation
of them that can be presented to the user.
Internet-draft February 2008
translation of them that can be presented to the user.
C: A001 LANGUAGE DE-IT C: A001 LANGUAGE DE-IT
S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION" S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION"
("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
"TRANSLATION" ("Gemeinsame Postf&AM8-cher/"))) "TRANSLATION" ("Gemeinsame Postf&AM8-cher/")))
S: A001 OK LANGUAGE-Befehl ausgefuehrt S: A001 OK LANGUAGE-Befehl ausgefuehrt
3.5 Formal Syntax 3.5. Formal Syntax
The following syntax specification inherits ABNF [RFC4234] rules The following syntax specification inherits ABNF [RFC5234] rules from
from IMAP4rev1 [RFC3501], IMAP4 Namespace [RFC2342], Tags for the IMAP4rev1 [RFC3501], IMAP4 Namespace [RFC2342], Tags for the
Identifying Languages [RFC4646], UTF-8 [RFC3629] and Collected Identifying Languages [RFC4646], UTF-8 [RFC3629], and Collected
Extensions to IMAP4 ABNF [RFC4466]. Extensions to IMAP4 ABNF [RFC4466].
command-any =/ language-cmd command-any =/ language-cmd
; LANGUAGE command is valid in all states ; LANGUAGE command is valid in all states
language-cmd = "LANGUAGE" *(SP lang-range-quoted) language-cmd = "LANGUAGE" *(SP lang-range-quoted)
response-payload =/ language-data response-payload =/ language-data
language-data = "LANGUAGE" SP "(" lang-tag-quoted *(SP language-data = "LANGUAGE" SP "(" lang-tag-quoted *(SP
skipping to change at page 8, line 5 skipping to change at page 9, line 5
resp-text = ["[" resp-text-code "]" SP ] UTF8-TEXT-CHAR resp-text = ["[" resp-text-code "]" SP ] UTF8-TEXT-CHAR
*(UTF8-TEXT-CHAR / "[") *(UTF8-TEXT-CHAR / "[")
; After the server is changed to a language other than ; After the server is changed to a language other than
; i-default, this resp-text rule replaces the resp-text ; i-default, this resp-text rule replaces the resp-text
; rule from [RFC3501]. ; rule from [RFC3501].
UTF8-TEXT-CHAR = %x20-5A / %x5C-7E / UTF8-2 / UTF8-3 / UTF8-4 UTF8-TEXT-CHAR = %x20-5A / %x5C-7E / UTF8-2 / UTF8-3 / UTF8-4
; UTF-8 excluding 7-bit control characters and "[" ; UTF-8 excluding 7-bit control characters and "["
Internet-draft February 2008
4. I18NLEVEL=1 and I18NLEVEL=2 Extensions 4. I18NLEVEL=1 and I18NLEVEL=2 Extensions
4.1 Introduction and Overview 4.1. Introduction and Overview
IMAP4rev1 [RFC3501] includes the SEARCH command which can be used to IMAP4rev1 [RFC3501] includes the SEARCH command that can be used to
locate messages matching criteria including human-readable text. locate messages matching criteria including human-readable text. The
The SORT extension [SORT] to IMAP allows the client to ask the SORT extension [SORT] to IMAP allows the client to ask the server to
server to determine the order of messages based on criteria determine the order of messages based on criteria including human-
including human-readable text. These mechanisms require the ability readable text. These mechanisms require the ability to support non-
to support non-English search and sort functions. English search and sort functions.
Section 4 defines two IMAP extensions for internationalizing IMAP Section 4 defines two IMAP extensions for internationalizing IMAP
SEARCH, SORT and THREAD [SORT] using the comparator framework SEARCH, SORT, and THREAD [SORT] using the comparator framework
[RFC4790]. [RFC4790].
The I18NLEVEL=1 extension updates SEARCH/SORT/THREAD to use The I18NLEVEL=1 extension updates SEARCH/SORT/THREAD to use
i;unicode-casemap comparator, as defined in [UCM]. See Sections 4.2 i;unicode-casemap comparator, as defined in [UCM]. See Sections 4.2
and 4.3 for more details. and 4.3 for more details.
The I18NLEVEL=2 extension is a superset of the I18NLEVEL=1 The I18NLEVEL=2 extension is a superset of the I18NLEVEL=1 extension.
extension. It adds to I18NLEVEL=1 extension the ability to determine It adds to I18NLEVEL=1 extension the ability to determine the active
the active comparator (see definition below) and negotiate use of comparator (see definition below) and to negotiate use of comparators
comparators using the COMPARATOR command. It also adds the using the COMPARATOR command. It also adds the COMPARATOR response
COMPARATOR response that indicates the active comparator and that indicates the active comparator and possibly other available
possibly other available comparators. See Sections 4.2 and 4.4 for comparators. See Sections 4.2 and 4.4 for more details.
more details.
4.2 Requirements common to both I18NLEVEL=1 and I18NLEVEL=2 4.2. Requirements Common to Both I18NLEVEL=1 and I18NLEVEL=2
The term "default comparator" refers to the comparator which is used The term "default comparator" refers to the comparator that is used
by SEARCH and SORT absent any negotiation using the COMPARATOR (see by SEARCH and SORT absent any negotiation using the COMPARATOR
Section 4.7) command. The term "active comparator" refers to the command (see Section 4.7). The term "active comparator" refers to
comparator which will be used within a session e.g. by SEARCH and the comparator which will be used within a session, e.g., by SEARCH
SORT. The COMPARATOR command is used to change the active and SORT. The COMPARATOR command is used to change the active
comparator. comparator.
The active comparator applies to the following SEARCH keys: "BCC", The active 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 active server also advertises the "SORT" extension, then the active
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 THREAD=ORDEREDSUBJECT, "SUBJECT", and "TO". If the server advertises THREAD=ORDEREDSUBJECT,
then the active comparator applies to the ORDEREDSUBJECT threading then the active comparator applies to the ORDEREDSUBJECT threading
algorithm. If the server advertises THREAD=REFERENCES, then the algorithm. If the server advertises THREAD=REFERENCES, then the
active comparator applies to the subject field comparisons done by active comparator applies to the subject field comparisons done by
REFERENCES threading algorithm. Future extensions may choose to REFERENCES threading algorithm. Future extensions may choose to
apply the active comparator to their SEARCH keys. apply the active comparator to their SEARCH keys.
Internet-draft February 2008 For SORT and THREAD, the pre-processing necessary to extract the base
subject text from a Subject header occurs prior to the application of
For SORT and THREAD, the pre-processing necessary to extract the a comparator.
base subject text from a Subject header occurs prior to the
application of a comparator.
A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST
implement the i;unicode-casemap comparator, as defined in [UCM]. implement the i;unicode-casemap comparator, as defined in [UCM].
A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST
support UTF-8 as a SEARCH charset. support UTF-8 as a SEARCH charset.
4.3 I18NLEVEL=1 Extension Requirements 4.3. I18NLEVEL=1 Extension Requirements
An IMAP server that satisfies all requirements specified in sections An IMAP server that satisfies all requirements specified in Sections
4.2 and 4.6 (and doesn't support/advertise any other I18NLEVEL=<n> 4.2 and 4.6 (and that doesn't support/advertise any other
extension, where n > 1) MUST list the keyword I18NLEVEL=1 in its I18NLEVEL=<n> extension, where n > 1) MUST list the keyword
CAPABILITY data once IMAP enters the authenticated state, and MAY I18NLEVEL=1 in its CAPABILITY data once IMAP enters the authenticated
list that keyword in other states. state, and MAY list that keyword in other states.
4.4 I18NLEVEL=2 Extension Requirements 4.4. I18NLEVEL=2 Extension Requirements
IMAP server that satisfies all requirements specified in sections An IMAP server that satisfies all requirements specified in Sections
4.2, 4.4, 4.6-4.10 (and doesn't support/advertise any other 4.2, 4.4, and 4.6-4.10 (and that doesn't support/advertise any other
I18NLEVEL=<n> extension, where n > 2) MUST list the keyword I18NLEVEL=<n> extension, where n > 2) MUST list the keyword
I18NLEVEL=2 in its CAPABILITY data once IMAP enters the I18NLEVEL=2 in its CAPABILITY data once IMAP enters the authenticated
authenticated state, and MAY list that keyword in other states. state, and MAY list that keyword in other states.
A server that advertises this extension MUST implement the A server that advertises this extension MUST implement the
i;unicode-casemap comparator, as defined in [UCM]. It MAY implement i;unicode-casemap comparator, as defined in [UCM]. It MAY implement
other comparators from the IANA registry established by [RFC4790]. other comparators from the IANA registry established by [RFC4790].
See also section 4.5 of this document. See also Section 4.5 of this document.
A server that advertises this extension SHOULD use i;unicode-casemap A server that advertises this extension SHOULD use i;unicode-casemap
as the default comparator. (Note that i;unicode-casemap is the as the default comparator. (Note that i;unicode-casemap is the
default comparator for I18NLEVEL=1, but not necessarily the default default comparator for I18NLEVEL=1, but not necessarily the default
for I18NLEVEL=2.) The selection of the default comparator MAY be for I18NLEVEL=2.) The selection of the default comparator MAY be
adjustable by the server administrator, and MAY be sensitive to the adjustable by the server administrator, and MAY be sensitive to the
current user. Once the IMAP connection enters authenticated state, current user. Once the IMAP connection enters authenticated state,
the default comparator MUST remain static for the remainder of that the default comparator MUST remain static for the remainder of that
connection. connection.
Note that since SEARCH uses the substring operation, IMAP servers Note that since SEARCH uses the substring operation, IMAP servers can
can only implement collations that offer the substring operation only implement collations that offer the substring operation (see
(see [RFC4790 section 4.2.2). Since SORT uses ordering operation [RFC4790], Section 4.2.2). Since SORT uses the ordering operation
(and by implication equality), IMAP servers which advertise the SORT (which in turn uses the equality operation), IMAP servers that
extension can only implement collations that offer all three advertise the SORT extension can only implement collations that offer
all three operations (see [RFC4790], Sections 4.2.2-4.2.4).
Internet-draft February 2008
operations (see [RFC4790] sections 4.2.2-4).
If the active collation does not provide the operations needed by an If the active collation does not provide the operations needed by an
IMAP command, the server MUST respond with a tagged BAD. IMAP command, the server MUST respond with a tagged BAD.
4.5 Compatibility Notes 4.5. Compatibility Notes
Several server implementations deployed prior to the publication of Several server implementations deployed prior to the publication of
this specification comply with I18NLEVEL=1 (see section 4.3), but do this specification comply with I18NLEVEL=1 (see Section 4.3), but do
not advertise that. Other legacy servers use the i;ascii-casemap not advertise that. Other legacy servers use the i;ascii-casemap
(see [RFC4790]) comparator. comparator (see [RFC4790]).
There is no good way for a client to know which comparator that a There is no good way for a client to know which comparator a legacy
legacy server uses. If the client has to assume the worst, it may server uses. If the client has to assume the worst, it may end up
end up doing expensive local operations to obtain i;unicode-casemap doing expensive local operations to obtain i;unicode-casemap
comparisons even though the server implements it. comparisons even though the server implements it.
Legacy server implementations which comply with I18NLEVEL=1 should Legacy server implementations which comply with I18NLEVEL=1 should be
be updated to advertise I18NLEVEL=1. All server implementations updated to advertise I18NLEVEL=1. All server implementations should
should eventually be updated to comply with the I18NLEVEL=2 eventually be updated to comply with the I18NLEVEL=2 extension.
extension.
4.6 Comparators and Character Encodings 4.6. Comparators and Character Encodings
RFC 3501, section 6.4.4 says: RFC 3501, Section 6.4.4, says:
In all search keys that use strings, a message matches In all search keys that use strings, a message matches the key
the key if the string is a substring of the field. The if the string is a substring of the field. The matching is
matching is case-insensitive. case-insensitive.
When performing the SEARCH operation, the active comparator is When performing the SEARCH operation, the active comparator is
applied instead of the case-insensitive matching specified above. applied instead of the case-insensitive matching specified above.
An IMAP server which performs collation operations (e.g., as part of An IMAP server which performs collation operations (e.g., as part of
commands such as SEARCH, SORT, THREAD) does so according to the commands such as SEARCH, SORT, and THREAD) does so according to the
following procedure: following procedure:
(a) MIME encoding (for example see [RFC2047] for headers and (a) MIME encoding (for example, see [RFC2047] for headers and
[RFC2045] for body parts) MUST be removed in the texts being [RFC2045] for body parts) MUST be removed in the texts being
collated. collated.
If MIME encoding removal fails for a message (e.g., a body part If MIME encoding removal fails for a message (e.g., a body part
of the message has an unsupported Content-Transfer-Encoding, of the message has an unsupported Content-Transfer-Encoding, uses
uses characters not allowed by the Content-Transfer-Encoding, characters not allowed by the Content-Transfer-Encoding, etc.),
etc.), the collation of this message is undefined by this the collation of this message is undefined by this specification,
specification, and is handled in an implementation-dependent and is handled in an implementation-dependent manner.
Internet-draft February 2008
manner.
(b) The decoded text from (a) MUST be converted to the charset (b) The decoded text from (a) MUST be converted to the charset
expected by the active comparator. expected by the active comparator.
(c) For the substring operation: (c) For the substring operation:
If step (b) failed (e.g., the text is in an unknown charset, If step (b) failed (e.g., the text is in an unknown charset,
contains a sequence which is not valid according in that contains a sequence that is not valid according in that charset,
charset, etc.), the original decoded text from (a) (i.e., etc.), the original decoded text from (a) (i.e., before the
before the charset conversion attempt) is collated using the charset conversion attempt) is collated using the i;octet
i;octet comparator (see [RFC4790]). comparator (see [RFC4790]).
If step (b) was successful, the converted text from (b) is If step (b) was successful, the converted text from (b) is
collated according to the active comparator. collated according to the active comparator.
For the ordering operation: For the ordering operation:
All strings that were successfully converted by step (b) are All strings that were successfully converted by step (b) are
separated from all strings that failed step (b). Strings in separated from all strings that failed step (b). Strings in each
each group are collated independently. All strings successfully group are collated independently. All strings successfully
converted by step (b) are then validated by the active converted by step (b) are then validated by the active
comparator. Strings that pass validation are collated using the comparator. Strings that pass validation are collated using the
active comparator. All strings that either fail step (b) or fail active comparator. All strings that either fail step (b) or fail
the active collation's validity operation are collated (after the active collation's validity operation are collated (after
applying step (a)) using the i;octet comparator (see [RFC4790]). applying step (a)) using the i;octet comparator (see [RFC4790]).
The resulting sorted list is produced by appending all collated The resulting sorted list is produced by appending all collated
"failed" strings after all strings collated using the active "failed" strings after all strings collated using the active
comparator. comparator.
Example: The following example demonstrates ordering of 4 Example: The following example demonstrates ordering of 4
different strings using i;unicode-casemap [UCM] comparator. different strings using the i;unicode-casemap [UCM] comparator.
Strings are represented using hexadecimal notation used by Strings are represented using hexadecimal notation used by ABNF
ABNF [RFC4234]. [RFC5234].
(1) %xD0 %xC0 %xD0 %xBD %xD0 %xB4 %xD1 %x80 %xD0 %xB5 (1) %xD0 %xC0 %xD0 %xBD %xD0 %xB4 %xD1 %x80 %xD0 %xB5
%xD0 %xB9 (labeled with charset=UTF-8) %xD0 %xB9 (labeled with charset=UTF-8)
(2) %xD1 %x81 %xD0 %x95 %xD0 %xA0 %xD0 %x93 %xD0 %x95 (2) %xD1 %x81 %xD0 %x95 %xD0 %xA0 %xD0 %x93 %xD0 %x95
%xD0 %x99 (labeled with charset=UTF-8) %xD0 %x99 (labeled with charset=UTF-8)
(3) %xD0 %x92 %xD0 %xB0 %xD1 %x81 %xD0 %xB8 %xD0 %xBB (3) %xD0 %x92 %xD0 %xB0 %xD1 %x81 %xD0 %xB8 %xD0 %xBB
%xD0 %xB8 %xFF %xB9 (labeled with charset=UTF-8) %xD0 %xB8 %xFF %xB9 (labeled with charset=UTF-8)
(4) %xE1 %xCC %xC5 %xCB %xD3 %xC5 %xCA (labeled with (4) %xE1 %xCC %xC5 %xCB %xD3 %xC5 %xCA (labeled with
charset=KOI8-R) charset=KOI8-R)
Step (b) will convert string # 4 to the following Step (b) will convert string (4) to the following sequence of
sequence of octets (in UTF-8): octets (in UTF-8):
Internet-draft February 2008
%xD0 %x90 %xD0 %xBB %xD0 %xB5 %xD0 %xBA %xD1 %x81 %xD0 %xD0 %x90 %xD0 %xBB %xD0 %xB5 %xD0 %xBA %xD1 %x81 %xD0
%xB5 %xD0 %xB9 %xB5 %xD0 %xB9
and will reject strings (1) and (3), as they contain and will reject strings (1) and (3), as they contain octets not
octets not allowed in charset=UTF-8. allowed in charset=UTF-8.
After that, using the i;unicode-casemap collation,
string (4) will collate before string (2). Using the After that, using the i;unicode-casemap collation, string (4)
i;octet collation on the original strings, string (3) will collate before string (2). Using the i;octet collation on
will collate before string (1). So the final ordering the original strings, string (3) will collate before string (1).
is as follows: (4) (2) (3) (1). So the final ordering is as follows: (4) (2) (3) (1).
If the substring operation (e.g., IMAP SEARCH) of the active If the substring operation (e.g., IMAP SEARCH) of the active
comparator returns the "undefined" result (see section 4.2.3 of comparator returns the "undefined" result (see Section 4.2.3 of
[RFC4790]) for either the text specified in the SEARCH command or [RFC4790]) for either the text specified in the SEARCH command or the
the message text, then the operation is repeated on the result of message text, then the operation is repeated on the result of step
step (a) using the i;octet comparator. (a) using the i;octet comparator.
The ordering operation (e.g., IMAP SORT and THREAD) SHOULD collate The ordering operation (e.g., IMAP SORT and THREAD) SHOULD collate
the following together: strings encoded using unknown or invalid the following together: strings encoded using unknown or invalid
character encodings, strings in unrecognized charsets, and invalid character encodings, strings in unrecognized charsets, and invalid
input (as defined by the active collation). input (as defined by the active collation).
4.7 COMPARATOR Command 4.7. COMPARATOR Command
Arguments: Optional comparator order arguments. Arguments: Optional comparator order arguments.
Response: A possible COMPARATOR response (see Section 4.8). Response: A possible COMPARATOR response (see Section 4.8).
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 valid in authenticated and selected The COMPARATOR command is valid in authenticated and selected states.
states.
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 results in a comparator. When issued with no arguments, it results in a
COMPARATOR response indicating the currently active comparator. COMPARATOR response indicating the currently active comparator.
When issued with one or more comparator argument, it changes the When issued with one or more comparator arguments, it changes the
active comparator as directed. (If more than one installed active comparator as directed. (If more than one installed
comparator is matched by an argument, the first argument wins.) The comparator is matched by an argument, the first argument wins.) The
COMPARATOR response lists all matching comparators if more than one COMPARATOR response lists all matching comparators if more than one
matches the specified patterns. matches the specified patterns.
The argument "default" refers to the server's default comparator. The argument "default" refers to the server's default comparator.
Otherwise, each argument is a collation specification as defined in
Internet-draft February 2008
Otherwise each argument is an collation specification as defined in
the Internet Application Protocol Comparator Registry [RFC4790]. the Internet Application Protocol Comparator Registry [RFC4790].
< The client requests activating a Czech comparator if possible, < The client requests activating a Czech comparator if possible,
or else a generic international comparator which it considers or else a generic international comparator which it considers
suitable for Czech. The server picks the first supported suitable for Czech. The server picks the first supported
comparator. > comparator. >
C: A001 COMPARATOR "cz;*" i;basic C: A001 COMPARATOR "cz;*" i;basic
S: * COMPARATOR i;basic S: * COMPARATOR i;basic
S: A001 OK Will use i;basic for collation S: A001 OK Will use i;basic for collation
4.8 COMPARATOR Response 4.8. COMPARATOR Response
Contents: The active comparator. Contents: The active comparator. An optional list of available
An optional list of available matching comparators 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.
4.9 BADCOMPARATOR response code 4.9. BADCOMPARATOR Response Code
This response code SHOULD be returned as a result of server failing This response code SHOULD be returned as a result of server failing
an IMAP command (returning NO), when the server knows that none of an IMAP command (returning NO), when the server knows that none of
the specified comparators match the requested comparator(s). the specified comparators match the requested comparator(s).
4.10 Formal Syntax 4.10. Formal Syntax
The following syntax specification inherits ABNF [RFC4234] rules The following syntax specification inherits ABNF [RFC5234] rules from
from IMAP4rev1 [RFC3501], and Internet Application Protocol IMAP4rev1 [RFC3501] and the Internet Application Protocol Comparator
Comparator Registry [RFC4790]. Registry [RFC4790].
command-auth =/ comparator-cmd command-auth =/ comparator-cmd
resp-text-code =/ "BADCOMPARATOR" resp-text-code =/ "BADCOMPARATOR"
comparator-cmd = "COMPARATOR" *(SP comp-order-quoted) comparator-cmd = "COMPARATOR" *(SP comp-order-quoted)
response-payload =/ comparator-data response-payload =/ comparator-data
comparator-data = "COMPARATOR" SP comp-sel-quoted [SP "(" comparator-data = "COMPARATOR" SP comp-sel-quoted [SP "("
comp-id-quoted *(SP comp-id-quoted) ")"] comp-id-quoted *(SP comp-id-quoted) ")"]
Internet-draft February 2008
comp-id-quoted = astring comp-id-quoted = astring
; Once any literal wrapper or quoting is removed, this ; Once any literal wrapper or quoting is removed, this
; follows the collation-id rule from [RFC4790] ; follows the collation-id rule from [RFC4790]
comp-order-quoted = astring comp-order-quoted = astring
; Once any literal wrapper or quoting is removed, this ; Once any literal wrapper or quoting is removed, this
; follows the collation-order rule from [RFC4790] ; follows the collation-order rule from [RFC4790]
comp-sel-quoted = astring comp-sel-quoted = astring
; Once any literal wrapper or quoting is removed, this ; Once any literal wrapper or quoting is removed, this
; follows the collation-selected rule from [RFC4790] ; follows the collation-selected rule from [RFC4790]
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 other standards work, such specification, but could be resolved by other standards work, such as
as that being done by the EAI group (see [IMAP-EAI]). that being done by the EAI working group (see [IMAP-EAI]).
5.1 Unicode Userids and Passwords 5.1. Unicode Userids and Passwords
IMAP4rev1 currently restricts the userid and password fields of the IMAP4rev1 currently restricts the userid and password fields of the
LOGIN command to US-ASCII. The "userid" and "password" fields of the LOGIN command to US-ASCII. The "userid" and "password" fields of the
IMAP LOGIN command are restricted to US-ASCII only until a future IMAP LOGIN command are restricted to US-ASCII only until a future
standards track RFC states otherwise. Servers are encouraged to standards track RFC states otherwise. Servers are encouraged to
validate both fields to make sure they conform to the formal syntax 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. 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 Servers MAY reject the LOGIN command if either the "userid" or
"password" field. "password" field contains an octet with the highest bit set.
When AUTHENTICATE is used, some servers may support userids and When AUTHENTICATE is used, some servers may support userids and
passwords in Unicode [RFC3490] since SASL (see [RFC4422]) allows passwords in Unicode [RFC3490] since SASL (see [RFC4422]) allows
that. However, such userids cannot be used as part of email that. However, such userids cannot be used as part of email
addresses. addresses.
5.2 UTF-8 Mailbox Names 5.2. UTF-8 Mailbox Names
The modified UTF-7 mailbox naming convention described in section The modified UTF-7 mailbox naming convention described in Section
5.1.3 of RFC 3501 is best viewed as an transition from the status 5.1.3 of RFC 3501 is best viewed as an transition from the status quo
quo in 1996 when modified UTF-7 was first specified. At that time, in 1996 when modified UTF-7 was first specified. At that time, there
there was widespread unofficial use of local character sets such as was widespread unofficial use of local character sets such as ISO-
ISO-8859-1 and Shift-JIS for non-ASCII mailbox names, with resultant 8859-1 and Shift-JIS for non-ASCII mailbox names, with resultant
non-interoperability. non-interoperability.
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
Internet-draft February 2008
we're ever going to be able to deploy UTF-8 mailbox names. Servers we're ever going to be able to deploy UTF-8 mailbox names. Servers
are encouraged to enforce them. are encouraged 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 [RFC3490]. While IMAP clients are free to support this Applications (IDNA)" [RFC3490]. While IMAP clients are free to
standard, an argument can be made that it would be helpful to simple support this standard, an argument can be made that it would be
clients if the IMAP server could perform this conversion (the same helpful to simple clients if the IMAP server could perform this
argument would apply to MIME header encoding [RFC2047]). However, conversion (the same argument would apply to MIME header encoding
it would be unwise to move forward with such work until the work in [RFC2047]). However, it would be unwise to move forward with such
progress to define the format of international email addresses is work until the work in progress to define the format of international
complete. email addresses is complete.
6. IANA Considerations 6. IANA Considerations
The IANA is requested to add LANGUAGE, I18NLEVEL=1 and I18NLEVEL=2 IANA added LANGUAGE, I18NLEVEL=1, and I18NLEVEL=2 to the IMAP4
to the IMAP4 Capabilities Registry. [Note to IANA: Capabilities Registry.
http://www.iana.org/assignments/imap4-capabilities]
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 root privilege when the server is in "Not Authenticated" state and do
do not revoke that privilege until after authentication is complete. 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.
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 that 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 re- messages themselves are subject to active attack. Clients MUST re-
issue the LANGUAGE command once a security layer is active, so this issue the LANGUAGE command once a security layer is active, in order
does not impact subsequent protocol operations. to prevent this attack from impacting subsequent protocol operations.
LANGUAGE, I18NLEVEL=1 and I18NLEVEL=2 extensions use the UTF-8 LANGUAGE, I18NLEVEL=1, and I18NLEVEL=2 extensions use the UTF-8
charset, thus the security considerations for UTF-8 [RFC3629] are charset; thus, the security considerations for UTF-8 [RFC3629] are
relevent. However, neither uses UTF-8 for identifiers so the most relevant. However, neither uses UTF-8 for identifiers, so the most
serious concerns do not apply. serious concerns do not apply.
8. Acknowledgements 8. Acknowledgements
Internet-draft February 2008 The LANGUAGE extension is based on a previous document by Mike
Gahrns, a substantial portion of the text in that section was written
The LANGUAGE extension is based on a previous Internet draft by Mike by him. Many people have participated in discussions about an IMAP
Gahrns, a substantial portion of the text in that section was Language extension in the various fora of the IETF and Internet
written by him. Many people have participated in discussions about working groups, so any list of contributors is bound to be
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 incomplete. However, the authors would like to thank Andrew McCown
for early work on the original proposal, John Myers for suggestions for early work on the original proposal, John Myers for suggestions
regarding the namespace issue, along with Jutta Degener, Mark regarding the namespace issue, along with Jutta Degener, Mark
Crispin, Mark Pustilnik, Larry Osterman, Cyrus Daboo, Martin Duerst, Crispin, Mark Pustilnik, Larry Osterman, Cyrus Daboo, Martin Duerst,
Timo Sirainen, Ben Campbell and Magnus Nystrom for their many Timo Sirainen, Ben Campbell, and Magnus Nystrom for their many
suggestions that have been incorporated into this document. suggestions that have been incorporated into this document.
Initial discussion of the I18NLEVEL=2 extension involved input from Initial discussion of the I18NLEVEL=2 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 Sources of Documents for Internationalized IMAP
Implementations
This is a non-normative list of standards to consider when This is a non-normative list of sources to consider when implementing
implementing i18n aware IMAP software. i18n-aware IMAP software.
o The LANGUAGE and I18NLEVEL=2 extensions to IMAP (this o The LANGUAGE and I18NLEVEL=2 extensions to IMAP (this
specification). specification).
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 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. RFC 3501.
o MIME [RFC2045] for message bodies. o MIME [RFC2045] for message bodies.
o MIME header encoding [RFC2047] for message headers. o MIME header encoding [RFC2047] for message headers.
o The IETF EAI working group. o The IETF EAI working group.
o MIME Parameter Value and Encoded Word Extensions [RFC2231] for o MIME Parameter Value and Encoded Word Extensions [RFC2231] for
filenames. Quality IMAP server implementations will filenames. Quality IMAP server implementations will
automatically combine multipart parameters when generating the automatically combine multipart parameters when generating the
BODYSTRUCTURE. There is also some deployed non-standard use of BODYSTRUCTURE. There is also some deployed non-standard use of
MIME header encoding inside double-quotes for filenames. MIME header encoding inside double quotes for filenames.
o IDNA [RFC3490] and punycode [RFC3492] for domain names o IDNA [RFC3490] and punycode [RFC3492] for domain names
(currently only relevant to IMAP clients). (currently only relevant to IMAP clients).
o The UTF-8 charset [RFC3629]. o The UTF-8 charset [RFC3629].
o The IETF policy on Character Sets and Languages [RFC2277]. o The IETF policy on Character Sets and Languages [RFC2277].
Normative References 10. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2277] Alvestrand, "IETF Policy on Character Sets and [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998. Languages", BCP 18, RFC 2277, January 1998.
Internet-draft February 2008 [RFC2342] Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342, May
1998.
[RFC2342] Gahrns, Newman, "IMAP4 Namespace", RFC 2342, May 1998.
[RFC3501] Crispin, "INTERNET MESSAGE ACCESS PROTOCOL - VERSION [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003. 4rev1", RFC 3501, March 2003.
[RFC3629] Yergeau, "UTF-8, a transformation format of ISO 10646", [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
STD 63, RFC 3629, November 2003. 10646", STD 63, RFC 3629, November 2003.
[RFC4234] Crocker, Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Specifications: ABNF", RFC 4234, Brandenburg Syntax Specifications: ABNF", STD 68, RFC 5234, January
Internetworking, Demon Internet Ltd, October 2005. 2008.
[RFC4422] Melnikov, Zeilenga, "Simple Authentication and Security [RFC4422] Melnikov, A., Ed., and K. Zeilenga, Ed., "Simple
Layer (SASL)", RFC 4422, June 2006. Authentication and Security Layer (SASL)", RFC 4422, June
2006.
[RFC4466] Melnikov, Daboo, "Collected Extensions to IMAP4 ABNF", [RFC4466] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4
RFC 4466, Isode Ltd., April 2006. ABNF", RFC 4466, April 2006.
[RFC4646] Philips, Davis, "Tags for Identifying Languages", BCP 47, [RFC4646] Phillips, A. and M. Davis, "Tags for Identifying
RFC 4646, September 2006. Languages", BCP 47, RFC 4646, September 2006.
[RFC4647] Philips, Davis, "Matching of Language Tags", BCP 47, RFC [RFC4647] Phillips, A. and M. Davis, "Matching of Language Tags",
4647, September 2006. BCP 47, RFC 4647, September 2006.
[RFC4790] Newman, Duerst, Gulbrandsen, "Internet Application [RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet
Protocol Comparator Registry", RFC 4790, February 2007. Application Protocol Collation Registry", RFC 4790, March
2007.
[SORT] Crispin, M. and K. Murchison, "INTERNET MESSAGE ACCESS [SORT] Crispin, M. and K. Murchison, "Internet Message Access
PROTOCOL - SORT AND THREAD EXTENSION", draft-ietf- Protocol - SORT and THREAD Extensions", RFC 5256, June
imapext-sort-19 (work in progress), November 2006. 2008.
[UCM] Crispin, "i;unicode-casemap - Simple Unicode Collation [UCM] Crispin, M., "i;unicode-casemap - Simple Unicode Collation
Algorithm", RFC 5051, October 2007. Algorithm", RFC 5051, October 2007.
[RFC2045] Freed, Borenstein, "Multipurpose Internet Mail Extensions [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
(MIME) Part One: Format of Internet Message Bodies", RFC Extensions (MIME) Part One: Format of Internet Message
2045, November 1996. Bodies", RFC 2045, November 1996.
[RFC2047] Moore, "MIME (Multipurpose Internet Mail Extensions) Part
Three: Message Header Extensions for Non-ASCII Text", RFC
2047, November 1996.
Informative References
[RFC2231] Freed, Moore, "MIME Parameter Value and Encoded Word [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
Extensions: Character Sets, Languages, and Part Three: Message Header Extensions for Non-ASCII Text",
RFC 2047, November 1996.
Internet-draft February 2008 11. Informative References
[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded
Word Extensions: Character Sets, Languages, and
Continuations", RFC 2231, November 1997. Continuations", RFC 2231, November 1997.
[RFC3490] Faltstrom, Hoffman, Costello, "Internationalizing Domain [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
Names in Applications (IDNA)", RFC 3490, March 2003. "Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003.
[RFC3492] Costello, "Punycode: A Bootstring encoding of Unicode for [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode
Internationalized Domain Names in Applications (IDNA)", for Internationalized Domain Names in Applications
RFC 3492, March 2003. (IDNA)", RFC 3492, March 2003.
[METADATA] Daboo, C., "IMAP METADATA Extension", draft-daboo-imap- [METADATA] Daboo, C., "IMAP METADATA Extension", Work in Progress,
annotatemore-12 (work in progress), December 2007. April 2008.
[IMAP-EAI] Resnick, Newman, "IMAP Support for UTF-8", draft-ietf- [IMAP-EAI] Resnick, P., and C. Newman, "IMAP Support for UTF-8", Work
eai-imap-utf8 (work in progress), May 2006. in Progress, November 2007.
Authors' Addresses Authors' Addresses
Chris Newman Chris Newman
Sun Microsystems Sun Microsystems
3401 Centrelake Dr., Suite 410 3401 Centrelake Dr., Suite 410
Ontario, CA 91761 Ontario, CA 91761
US US
Email: chris.newman@sun.com EMail: chris.newman@sun.com
Arnt Gulbrandsen Arnt Gulbrandsen
Oryx Mail Systems GmbH Oryx Mail Systems GmbH
Schweppermannstr. 8 Schweppermannstr. 8
D-81671 Muenchen D-81671 Muenchen
Germany Germany
Email: arnt@oryx.com EMail: arnt@oryx.com
Fax: +49 89 4502 9758 Fax: +49 89 4502 9758
Alexey Melnikov Alexey Melnikov
Isode Limited Isode Limited
5 Castle Business Village, 36 Station Road, 5 Castle Business Village, 36 Station Road,
Hampton, Middlesex, TW12 2BX, UK Hampton, Middlesex, TW12 2BX, UK
Email: Alexey.Melnikov@isode.com EMail: Alexey.Melnikov@isode.com
Internet-draft February 2008 Full Copyright Statement
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Full Copyright Statement
Copyright (C) The IETF Trust (2008). This document is subject to
the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL
WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY
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