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+Network Working Group A. Melnikov
+Request for Comments: 4466 Isode Ltd.
+Updates: 2088, 2342, 3501, 3502, 3516 C. Daboo
+Category: Standards Track April 2006
+
+
+ Collected Extensions to IMAP4 ABNF
+
+Status of This Memo
+
+ This document specifies an Internet standards track protocol for the
+ Internet community, and requests discussion and suggestions for
+ improvements. Please refer to the current edition of the "Internet
+ Official Protocol Standards" (STD 1) for the standardization state
+ and status of this protocol. Distribution of this memo is unlimited.
+
+Copyright Notice
+
+ Copyright (C) The Internet Society (2006).
+
+Abstract
+
+ Over the years, many documents from IMAPEXT and LEMONADE working
+ groups, as well as many individual documents, have added syntactic
+ extensions to many base IMAP commands described in RFC 3501. For
+ ease of reference, this document collects most of such ABNF changes
+ in one place.
+
+ This document also suggests a set of standard patterns for adding
+ options and extensions to several existing IMAP commands defined in
+ RFC 3501. The patterns provide for compatibility between existing
+ and future extensions.
+
+ This document updates ABNF in RFCs 2088, 2342, 3501, 3502, and 3516.
+ It also includes part of the errata to RFC 3501. This document
+ doesn't specify any semantic changes to the listed RFCs.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Melnikov & Daboo Standards Track [Page 1]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+Table of Contents
+
+ 1. Introduction ....................................................2
+ 1.1. Purpose of This Document ...................................2
+ 1.2. Conventions Used in This Document ..........................3
+ 2. IMAP ABNF Extensions ............................................3
+ 2.1. Optional Parameters with the SELECT/EXAMINE Commands .......3
+ 2.2. Extended CREATE Command ....................................4
+ 2.3. Extended RENAME Command ....................................5
+ 2.4. Extensions to FETCH and UID FETCH Commands .................6
+ 2.5. Extensions to STORE and UID STORE Commands .................6
+ 2.6. Extensions to SEARCH Command ...............................7
+ 2.6.1. Extended SEARCH Command .............................7
+ 2.6.2. ESEARCH untagged response ...........................8
+ 2.7. Extensions to APPEND Command ...............................8
+ 3. Formal Syntax ...................................................9
+ 4. Security Considerations ........................................14
+ 5. Normative References ...........................................15
+ 6. Acknowledgements ...............................................15
+
+1. Introduction
+
+1.1. Purpose of This Document
+
+ This document serves several purposes:
+
+ 1. rationalize and generalize ABNF for some existing IMAP
+ extensions;
+ 2. collect the ABNF in one place in order to minimize cross
+ references between documents;
+ 3. define building blocks for future extensions so that they can
+ be used together in a compatible way.
+
+ It is expected that a future revision of this document will be
+ incorporated into a revision of RFC 3501.
+
+ This document updates ABNF in RFCs 2088, 2342, 3501, 3502, and 3516.
+ It also includes part of the errata to RFC 3501. This document
+ doesn't specify any semantic changes to the listed RFCs.
+
+ The ABNF in section 6 of RFC 2342 got rewritten to conform to the
+ ABNF syntax as defined in RFC 4234 and to reference new non-terminals
+ from RFC 3501. It was also restructured to allow for better
+ readability. There were no changes "on the wire".
+
+ Section 2 extends ABNF for SELECT, EXAMINE, CREATE, RENAME, FETCH/UID
+ FETCH, STORE/UID STORE, SEARCH, and APPEND commands in a consistent
+ manner. Extensions to all the commands but APPEND have the same
+
+
+
+Melnikov & Daboo Standards Track [Page 2]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+ structure. Extensibility for the APPEND command was done slightly
+ differently in order to preserve backward compatibility with existing
+ extensions.
+
+ Section 2 also defines a new ESEARCH response, whose purpose is to
+ define a better version of the SEARCH response defined in RFC 3501.
+
+ Section 3 defines the collected ABNF that replaces pieces of ABNF in
+ the aforementioned RFCs. The collected ABNF got generalized to allow
+ for easier future extensibility.
+
+1.2. Conventions Used in This Document
+
+ In examples, "C:" and "S:" indicate lines sent by the client and
+ server, respectively.
+
+ The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
+ in this document are to be interpreted as defined in "Key words for
+ use in RFCs to Indicate Requirement Levels" [KEYWORDS].
+
+2. IMAP ABNF Extensions
+
+ This section is not normative. It provides some background on the
+ intended use of different extensions and it gives some guidance about
+ how future extensions should extend the described commands.
+
+2.1. Optional Parameters with the SELECT/EXAMINE Commands
+
+ This document adds the ability to include one or more parameters with
+ the IMAP SELECT (section 6.3.1 of [IMAP4]) or EXAMINE (section 6.3.2
+ of [IMAP4]) commands, to turn on or off certain standard behaviors,
+ or to add new optional behaviors required for a particular extension.
+
+ There are two possible modes of operation:
+
+ o A global state change where a single use of the optional parameter
+ will affect the session state from that time on, irrespective of
+ subsequent SELECT/EXAMINE commands.
+
+ o A per-mailbox state change that will affect the session only for
+ the duration of the new selected state. A subsequent
+ SELECT/EXAMINE without the optional parameter will cancel its
+ effect for the newly selected mailbox.
+
+ Optional parameters to the SELECT or EXAMINE commands are added as a
+ parenthesized list of attribute/value pairs, and appear after the
+ mailbox name in the standard SELECT or EXAMINE command. The order of
+ individual parameters is arbitrary. A parameter value is optional
+
+
+
+Melnikov & Daboo Standards Track [Page 3]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+ and may consist of atoms, strings, or lists in a specific order. If
+ the parameter value is present, it always appears in parentheses (*).
+ Any parameter not defined by extensions that the server supports must
+ be rejected with a BAD response.
+
+ Example:
+
+ C: a SELECT INBOX (ANNOTATE)
+ S: ...
+ S: a OK SELECT complete
+
+ In the above example, a single parameter is used with the SELECT
+ command.
+
+ Example:
+
+ C: a EXAMINE INBOX (ANNOTATE RESPONSES ("UID Responses")
+ CONDSTORE)
+ S: ...
+ S: a OK EXAMINE complete
+
+ In the above example, three parameters are used with the EXAMINE
+ command. The second parameter consists of two items: an atom
+ "RESPONSES" followed by a quoted string.
+
+ Example:
+
+ C: a SELECT INBOX (BLURDYBLOOP)
+ S: a BAD Unknown parameter in SELECT command
+
+ In the above example, a parameter not supported by the server is
+ used. This results in the BAD response from the server.
+
+ (*) - if a parameter has a mandatory value, which can always be
+ represented as a number or a sequence-set, the parameter value does
+ not need the enclosing (). See ABNF for more details.
+
+2.2. Extended CREATE Command
+
+ Arguments: mailbox name
+ OPTIONAL list of CREATE parameters
+
+ Responses: no specific responses for this command
+
+ Result: OK - create completed
+ NO - create failure: cannot create mailbox with
+ that name
+ BAD - argument(s) invalid
+
+
+
+Melnikov & Daboo Standards Track [Page 4]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+ This document adds the ability to include one or more parameters with
+ the IMAP CREATE command (see section 6.3.3 of [IMAP4]), to turn on or
+ off certain standard behaviors, or to add new optional behaviors
+ required for a particular extension. No CREATE parameters are
+ defined in this document.
+
+ Optional parameters to the CREATE command are added as a
+ parenthesized list of attribute/value pairs after the mailbox name.
+ The order of individual parameters is arbitrary. A parameter value
+ is optional and may consist of atoms, strings, or lists in a specific
+ order. If the parameter value is present, it always appears in
+ parentheses (*). Any parameter not defined by extensions that the
+ server supports must be rejected with a BAD response.
+
+ (*) - if a parameter has a mandatory value, which can always be
+ represented as a number or a sequence-set, the parameter value does
+ not need the enclosing (). See ABNF for more details.
+
+2.3. Extended RENAME Command
+
+ Arguments: existing mailbox name
+ new mailbox name
+ OPTIONAL list of RENAME parameters
+
+ Responses: no specific responses for this command
+
+ Result: OK - rename completed
+ NO - rename failure: cannot rename mailbox with
+ that name, cannot rename to mailbox with
+ that name, etc.
+ BAD - argument(s) invalid
+
+ This document adds the ability to include one or more parameters with
+ the IMAP RENAME command (see section 6.3.5 of [IMAP4]), to turn on or
+ off certain standard behaviors, or to add new optional behaviors
+ required for a particular extension. No RENAME parameters are
+ defined in this document.
+
+ Optional parameters to the RENAME command are added as a
+ parenthesized list of attribute/value pairs after the new mailbox
+ name. The order of individual parameters is arbitrary. A parameter
+ value is optional and may consist of atoms, strings, or lists in a
+ specific order. If the parameter value is present, it always appears
+ in parentheses (*). Any parameter not defined by extensions that the
+ server supports must be rejected with a BAD response.
+
+
+
+
+
+
+Melnikov & Daboo Standards Track [Page 5]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+ (*) - if a parameter has a mandatory value, which can always be
+ represented as a number or a sequence-set, the parameter value does
+ not need the enclosing (). See ABNF for more details.
+
+2.4. Extensions to FETCH and UID FETCH Commands
+
+ Arguments: sequence set
+ message data item names or macro
+ OPTIONAL fetch modifiers
+
+ Responses: untagged responses: FETCH
+
+ Result: OK - fetch completed
+ NO - fetch error: cannot fetch that data
+ BAD - command unknown or arguments invalid
+
+ This document extends the syntax of the FETCH and UID FETCH commands
+ (see section 6.4.5 of [IMAP4]) to include optional FETCH modifiers.
+ No fetch modifiers are defined in this document.
+
+ The order of individual modifiers is arbitrary. Each modifier is an
+ attribute/value pair. A modifier value is optional and may consist
+ of atoms and/or strings and/or lists in a specific order. If the
+ modifier value is present, it always appears in parentheses (*). Any
+ modifiers not defined by extensions that the server supports must be
+ rejected with a BAD response.
+
+ (*) - if a modifier has a mandatory value, which can always be
+ represented as a number or a sequence-set, the modifier value does
+ not need the enclosing (). See ABNF for more details.
+
+2.5. Extensions to STORE and UID STORE Commands
+
+ Arguments: message set
+ OPTIONAL store modifiers
+ message data item name
+ value for message data item
+
+ Responses: untagged responses: FETCH
+
+ Result: OK - store completed
+ NO - store error: cannot store that data
+ BAD - command unknown or arguments invalid
+
+ This document extends the syntax of the STORE and UID STORE commands
+ (see section 6.4.6 of [IMAP4]) to include optional STORE modifiers.
+ No store modifiers are defined in this document.
+
+
+
+
+Melnikov & Daboo Standards Track [Page 6]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+ The order of individual modifiers is arbitrary. Each modifier is an
+ attribute/value pair. A modifier value is optional and may consist
+ of atoms and/or strings and/or lists in a specific order. If the
+ modifier value is present, it always appears in parentheses (*). Any
+ modifiers not defined by extensions that the server supports must be
+ rejected with a BAD response.
+
+ (*) - if a modifier has a mandatory value, which can always be
+ represented as a number or a sequence-set, the modifier value does
+ not need the enclosing (). See ABNF for more details.
+
+2.6. Extensions to SEARCH Command
+
+2.6.1. Extended SEARCH Command
+
+ Arguments: OPTIONAL result specifier
+ OPTIONAL [CHARSET] specification
+ searching criteria (one or more)
+
+ Responses: REQUIRED untagged response: SEARCH (*)
+
+ Result: OK - search completed
+ NO - search error: cannot search that [CHARSET] or
+ criteria
+ BAD - command unknown or arguments invalid
+
+ This section updates definition of the SEARCH command described in
+ section 6.4.4 of [IMAP4].
+
+ The SEARCH command is extended to allow for result options. This
+ document does not define any result options.
+
+ The order of individual options is arbitrary. Individual options may
+ contain parameters enclosed in parentheses (**). If an option has
+ parameters, they consist of atoms and/or strings and/or lists in a
+ specific order. Any options not defined by extensions that the
+ server supports must be rejected with a BAD response.
+
+ (*) - An extension to the SEARCH command may require another untagged
+ response, or no untagged response to be returned. Section 2.6.2
+ defines a new ESEARCH untagged response that replaces the SEARCH
+ untagged response. Note that for a given extended SEARCH command the
+ SEARCH and ESEARCH responses SHOULD be mutually exclusive, i.e., only
+ one of them should be returned.
+
+ (**) - if an option has a mandatory parameter, which can always be
+ represented as a number or a sequence-set, the option parameter does
+ not need the enclosing (). See ABNF for more details.
+
+
+
+Melnikov & Daboo Standards Track [Page 7]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+2.6.2. ESEARCH untagged response
+
+ Contents: one or more search-return-data pairs
+
+ The ESEARCH response SHOULD be sent as a result of an extended SEARCH
+ or UID SEARCH command specified in section 2.6.1.
+
+ The ESEARCH response starts with an optional search correlator. If
+ it is missing, then the response was not caused by a particular IMAP
+ command, whereas if it is present, it contains the tag of the command
+ that caused the response to be returned.
+
+ The search correlator is followed by an optional UID indicator. If
+ this indicator is present, all data in the ESEARCH response refers to
+ UIDs, otherwise all returned data refers to message numbers.
+
+ The rest of the ESEARCH response contains one or more search data
+ pairs. Each pair starts with unique return item name, followed by a
+ space and the corresponding data. Search data pairs may be returned
+ in any order. Unless specified otherwise by an extension, any return
+ item name SHOULD appear only once in an ESEARCH response.
+
+ Example: S: * ESEARCH UID COUNT 5 ALL 4:19,21,28
+
+ Example: S: * ESEARCH (TAG "a567") UID COUNT 5 ALL 4:19,21,28
+
+ Example: S: * ESEARCH COUNT 5 ALL 1:17,21
+
+2.7. Extensions to APPEND Command
+
+ The IMAP BINARY extension [BINARY] extends the APPEND command to
+ allow a client to append data containing NULs by using the <literal8>
+ syntax. The ABNF was rewritten to allow for easier extensibility by
+ IMAP extensions. This document hasn't specified any semantical
+ changes to the [BINARY] extension.
+
+ In addition, the non-terminal "literal8" defined in [BINARY] got
+ extended to allow for non-synchronizing literals if both [BINARY] and
+ [LITERAL+] extensions are supported by the server.
+
+ The IMAP MULTIAPPEND extension [MULTIAPPEND] extends the APPEND
+ command to allow a client to append multiple messages atomically.
+ This document defines a common syntax for the APPEND command that
+ takes into consideration syntactic extensions defined by both
+ [BINARY] and [MULTIAPPEND] extensions.
+
+
+
+
+
+
+Melnikov & Daboo Standards Track [Page 8]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+3. Formal Syntax
+
+ The following syntax specification uses the Augmented Backus-Naur
+ Form (ABNF) notation as specified in [ABNF].
+
+ Non-terminals referenced but not defined below are as defined by
+ [IMAP4].
+
+ Except as noted otherwise, all alphabetic characters are case-
+ insensitive. The use of uppercase or lowercase characters to define
+ token strings is for editorial clarity only. Implementations MUST
+ accept these strings in a case-insensitive fashion.
+
+ append = "APPEND" SP mailbox 1*append-message
+ ;; only a single append-message may appear
+ ;; if MULTIAPPEND [MULTIAPPEND] capability
+ ;; is not present
+
+ append-message = append-opts SP append-data
+
+ append-ext = append-ext-name SP append-ext-value
+ ;; This non-terminal define extensions to
+ ;; to message metadata.
+
+ append-ext-name = tagged-ext-label
+
+ append-ext-value= tagged-ext-val
+ ;; This non-terminal shows recommended syntax
+ ;; for future extensions.
+
+
+ append-data = literal / literal8 / append-data-ext
+
+ append-data-ext = tagged-ext
+ ;; This non-terminal shows recommended syntax
+ ;; for future extensions,
+ ;; i.e., a mandatory label followed
+ ;; by parameters.
+
+ append-opts = [SP flag-list] [SP date-time] *(SP append-ext)
+ ;; message metadata
+
+ charset = atom / quoted
+ ;; Exact syntax is defined in [CHARSET].
+
+ create = "CREATE" SP mailbox
+ [create-params]
+ ;; Use of INBOX gives a NO error.
+
+
+
+Melnikov & Daboo Standards Track [Page 9]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+ create-params = SP "(" create-param *( SP create-param) ")"
+
+ create-param-name = tagged-ext-label
+
+ create-param = create-param-name [SP create-param-value]
+
+ create-param-value= tagged-ext-val
+ ;; This non-terminal shows recommended syntax
+ ;; for future extensions.
+
+
+ esearch-response = "ESEARCH" [search-correlator] [SP "UID"]
+ *(SP search-return-data)
+ ;; Note that SEARCH and ESEARCH responses
+ ;; SHOULD be mutually exclusive,
+ ;; i.e., only one of the response types
+ ;; should be
+ ;; returned as a result of a command.
+
+
+ examine = "EXAMINE" SP mailbox [select-params]
+ ;; modifies the original IMAP EXAMINE command
+ ;; to accept optional parameters
+
+ fetch = "FETCH" SP sequence-set SP ("ALL" / "FULL" /
+ "FAST" / fetch-att /
+ "(" fetch-att *(SP fetch-att) ")")
+ [fetch-modifiers]
+ ;; modifies the original IMAP4 FETCH command to
+ ;; accept optional modifiers
+
+ fetch-modifiers = SP "(" fetch-modifier *(SP fetch-modifier) ")"
+
+ fetch-modifier = fetch-modifier-name [ SP fetch-modif-params ]
+
+ fetch-modif-params = tagged-ext-val
+ ;; This non-terminal shows recommended syntax
+ ;; for future extensions.
+
+ fetch-modifier-name = tagged-ext-label
+
+ literal8 = "~{" number ["+"] "}" CRLF *OCTET
+ ;; A string that might contain NULs.
+ ;; <number> represents the number of OCTETs
+ ;; in the response string.
+ ;; The "+" is only allowed when both LITERAL+ and
+ ;; BINARY extensions are supported by the server.
+
+
+
+
+Melnikov & Daboo Standards Track [Page 10]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+ mailbox-data =/ Namespace-Response /
+ esearch-response
+
+ Namespace = nil / "(" 1*Namespace-Descr ")"
+
+ Namespace-Command = "NAMESPACE"
+
+ Namespace-Descr = "(" string SP
+ (DQUOTE QUOTED-CHAR DQUOTE / nil)
+ *(Namespace-Response-Extension) ")"
+
+ Namespace-Response-Extension = SP string SP
+ "(" string *(SP string) ")"
+
+ Namespace-Response = "NAMESPACE" SP Namespace
+ SP Namespace SP Namespace
+ ;; This response is currently only allowed
+ ;; if the IMAP server supports [NAMESPACE].
+ ;; The first Namespace is the Personal Namespace(s)
+ ;; The second Namespace is the Other Users' Namespace(s)
+ ;; The third Namespace is the Shared Namespace(s)
+
+ rename = "RENAME" SP mailbox SP mailbox
+ [rename-params]
+ ;; Use of INBOX as a destination gives
+ ;; a NO error, unless rename-params
+ ;; is not empty.
+
+ rename-params = SP "(" rename-param *( SP rename-param) ")"
+
+ rename-param = rename-param-name [SP rename-param-value]
+
+ rename-param-name = tagged-ext-label
+
+ rename-param-value= tagged-ext-val
+ ;; This non-terminal shows recommended syntax
+ ;; for future extensions.
+
+
+ response-data = "*" SP response-payload CRLF
+
+ response-payload= resp-cond-state / resp-cond-bye /
+ mailbox-data / message-data / capability-data
+
+ search = "SEARCH" [search-return-opts]
+ SP search-program
+
+ search-correlator = SP "(" "TAG" SP tag-string ")"
+
+
+
+Melnikov & Daboo Standards Track [Page 11]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+ search-program = ["CHARSET" SP charset SP]
+ search-key *(SP search-key)
+ ;; CHARSET argument to SEARCH MUST be
+ ;; registered with IANA.
+
+ search-return-data = search-modifier-name SP search-return-value
+ ;; Note that not every SEARCH return option
+ ;; is required to have the corresponding
+ ;; ESEARCH return data.
+
+ search-return-opts = SP "RETURN" SP "(" [search-return-opt
+ *(SP search-return-opt)] ")"
+
+ search-return-opt = search-modifier-name [SP search-mod-params]
+
+ search-return-value = tagged-ext-val
+ ;; Data for the returned search option.
+ ;; A single "nz-number"/"number" value
+ ;; can be returned as an atom (i.e., without
+ ;; quoting). A sequence-set can be returned
+ ;; as an atom as well.
+
+ search-modifier-name = tagged-ext-label
+
+ search-mod-params = tagged-ext-val
+ ;; This non-terminal shows recommended syntax
+ ;; for future extensions.
+
+
+ select = "SELECT" SP mailbox [select-params]
+ ;; modifies the original IMAP SELECT command to
+ ;; accept optional parameters
+
+ select-params = SP "(" select-param *(SP select-param) ")"
+
+ select-param = select-param-name [SP select-param-value]
+ ;; a parameter to SELECT may contain one or
+ ;; more atoms and/or strings and/or lists.
+
+ select-param-name= tagged-ext-label
+
+ select-param-value= tagged-ext-val
+ ;; This non-terminal shows recommended syntax
+ ;; for future extensions.
+
+
+ status-att-list = status-att-val *(SP status-att-val)
+ ;; Redefines status-att-list from RFC 3501.
+
+
+
+Melnikov & Daboo Standards Track [Page 12]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+ ;; status-att-val is defined in RFC 3501 errata
+
+ status-att-val = ("MESSAGES" SP number) /
+ ("RECENT" SP number) /
+ ("UIDNEXT" SP nz-number) /
+ ("UIDVALIDITY" SP nz-number) /
+ ("UNSEEN" SP number)
+ ;; Extensions to the STATUS responses
+ ;; should extend this production.
+ ;; Extensions should use the generic
+ ;; syntax defined by tagged-ext.
+
+ store = "STORE" SP sequence-set [store-modifiers]
+ SP store-att-flags
+ ;; extend [IMAP4] STORE command syntax
+ ;; to allow for optional store-modifiers
+
+ store-modifiers = SP "(" store-modifier *(SP store-modifier)
+ ")"
+
+ store-modifier = store-modifier-name [SP store-modif-params]
+
+ store-modif-params = tagged-ext-val
+ ;; This non-terminal shows recommended syntax
+ ;; for future extensions.
+
+ store-modifier-name = tagged-ext-label
+
+ tag-string = string
+ ;; tag of the command that caused
+ ;; the ESEARCH response, sent as
+ ;; a string.
+
+ tagged-ext = tagged-ext-label SP tagged-ext-val
+ ;; recommended overarching syntax for
+ ;; extensions
+
+ tagged-ext-label = tagged-label-fchar *tagged-label-char
+ ;; Is a valid RFC 3501 "atom".
+
+ tagged-label-fchar = ALPHA / "-" / "_" / "."
+
+ tagged-label-char = tagged-label-fchar / DIGIT / ":"
+
+
+
+
+
+
+
+
+Melnikov & Daboo Standards Track [Page 13]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+ tagged-ext-comp = astring /
+ tagged-ext-comp *(SP tagged-ext-comp) /
+ "(" tagged-ext-comp ")"
+ ;; Extensions that follow this general
+ ;; syntax should use nstring instead of
+ ;; astring when appropriate in the context
+ ;; of the extension.
+ ;; Note that a message set or a "number"
+ ;; can always be represented as an "atom".
+ ;; An URL should be represented as
+ ;; a "quoted" string.
+
+ tagged-ext-simple = sequence-set / number
+
+ tagged-ext-val = tagged-ext-simple /
+ "(" [tagged-ext-comp] ")"
+
+4. Security Considerations
+
+ This document updates ABNF in RFCs 2088, 2342, 3501, 3502, and 3516.
+ The updated documents must be consulted for security considerations
+ for the extensions that they define.
+
+ As a protocol gets more complex, parser bugs become more common
+ including buffer overflow, denial of service, and other common
+ security coding errors. To the extent that this document makes the
+ parser more complex, it makes this situation worse. To the extent
+ that this document makes the parser more consistent and thus simpler,
+ the situation is improved. The impact will depend on how many
+ deployed IMAP extensions are consistent with this document.
+ Implementers are encouraged to take care of these issues when
+ extending existing implementations. Future IMAP extensions should
+ strive for consistency and simplicity to the greatest extent
+ possible.
+
+ Extensions to IMAP commands that are permitted in NOT AUTHENTICATED
+ state are more sensitive to these security issues due to the larger
+ possible attacker community prior to authentication, and the fact
+ that some IMAP servers run with elevated privileges in that state.
+ This document does not extend any commands permitted in NOT
+ AUTHENTICATED state. Future IMAP extensions to commands permitted in
+ NOT AUTHENTICATED state should favor simplicity over consistency or
+ extensibility.
+
+
+
+
+
+
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+
+Melnikov & Daboo Standards Track [Page 14]
+
+RFC 4466 Collected Extensions to IMAP4 ABNF April 2006
+
+
+5. Normative References
+
+ [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+ [IMAP4] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL -
+ VERSION 4rev1", RFC 3501, March 2003.
+
+ [ABNF] Crocker, D., Ed., and P. Overell, "Augmented BNF for
+ Syntax Specifications: ABNF", RFC 4234, October 2005.
+
+ [CHARSET] Freed, N. and J. Postel, "IANA Charset Registration
+ Procedures", BCP 19, RFC 2978, October 2000.
+
+ [MULTIAPPEND] Crispin, M., "Internet Message Access Protocol (IMAP) -
+ MULTIAPPEND Extension", RFC 3502, March 2003.
+
+ [NAMESPACE] Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342,
+ May 1998.
+
+ [LITERAL+] Myers, J., "IMAP4 non-synchronizing literals", RFC
+ 2088, January 1997.
+
+ [BINARY] Nerenberg, L., "IMAP4 Binary Content Extension", RFC
+ 3516, April 2003.
+
+6. Acknowledgements
+
+ This documents is based on ideas proposed by Pete Resnick, Mark
+ Crispin, Ken Murchison, Philip Guenther, Randall Gellens, and Lyndon
+ Nerenberg.
+
+ However, all errors and omissions must be attributed to the authors
+ of the document.
+
+ Thanks to Philip Guenther, Dave Cridland, Mark Crispin, Chris Newman,
+ Elwyn Davies, and Barry Leiba for comments and corrections.
+
+ literal8 syntax was taken from RFC 3516.
+
+
+
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+Melnikov & Daboo Standards Track [Page 15]
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+
+
+Authors' Addresses
+
+ Alexey Melnikov
+ Isode Limited
+ 5 Castle Business Village
+ 36 Station Road
+ Hampton, Middlesex, TW12 2BX
+ UK
+
+ EMail: Alexey.Melnikov@isode.com
+
+
+ Cyrus Daboo
+
+ EMail: cyrus@daboo.name
+
+
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+
+Full Copyright Statement
+
+ Copyright (C) The Internet Society (2006).
+
+ 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 AND THE INTERNET
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+ INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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+
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+
+Acknowledgement
+
+ Funding for the RFC Editor function is provided by the IETF
+ Administrative Support Activity (IASA).
+
+
+
+
+
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+
+Melnikov & Daboo Standards Track [Page 17]
+