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Network Working Group C. Daboo Request for Comments: 5464 Apple, Inc. Category: Standards Track February 2009

                    The IMAP METADATA Extension

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.

Abstract

 The METADATA extension to the Internet Message Access Protocol
 permits clients and servers to maintain "annotations" or "metadata"
 on IMAP servers.  It is possible to have annotations on a per-mailbox
 basis or on the server as a whole.  For example, this would allow
 comments about the purpose of a particular mailbox to be "attached"
 to that mailbox, or a "message of the day" containing server status
 information to be made available to anyone logging in to the server.

Daboo Standards Track [Page 1] RFC 5464 The IMAP METADATA Extension February 2009

Table of Contents

 1.  Introduction and Overview  . . . . . . . . . . . . . . . . . .  3
 2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
 3.  Data Model . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.2.  Namespace of Entries . . . . . . . . . . . . . . . . . . .  4
     3.2.1.  Entry Names  . . . . . . . . . . . . . . . . . . . . .  5
   3.3.  Private versus Shared and Access Control . . . . . . . . .  6
 4.  IMAP Protocol Changes  . . . . . . . . . . . . . . . . . . . .  7
   4.1.  General Considerations . . . . . . . . . . . . . . . . . .  7
   4.2.  GETMETADATA Command  . . . . . . . . . . . . . . . . . . .  8
     4.2.1.  MAXSIZE GETMETADATA Command Option . . . . . . . . . .  9
     4.2.2.  DEPTH GETMETADATA Command Option . . . . . . . . . . . 10
   4.3.  SETMETADATA Command  . . . . . . . . . . . . . . . . . . . 10
   4.4.  METADATA Response  . . . . . . . . . . . . . . . . . . . . 12
     4.4.1.  METADATA Response with Values  . . . . . . . . . . . . 13
     4.4.2.  Unsolicited METADATA Response without Values . . . . . 13
 5.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . . 14
 6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   6.1.  Entry and Attribute Registration Template  . . . . . . . . 16
   6.2.  Server Entry Registrations . . . . . . . . . . . . . . . . 16
     6.2.1.  /shared/comment  . . . . . . . . . . . . . . . . . . . 17
     6.2.2.  /shared/admin  . . . . . . . . . . . . . . . . . . . . 17
   6.3.  Mailbox Entry Registrations  . . . . . . . . . . . . . . . 17
     6.3.1.  /shared/comment  . . . . . . . . . . . . . . . . . . . 18
     6.3.2.  /private/comment . . . . . . . . . . . . . . . . . . . 18
 7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
 8.  Normative References . . . . . . . . . . . . . . . . . . . . . 19
 Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 19

Daboo Standards Track [Page 2] RFC 5464 The IMAP METADATA Extension February 2009

1. Introduction and Overview

 The goal of the METADATA extension is to provide a means for clients
 to set and retrieve "annotations" or "metadata" on an IMAP server.
 The annotations can be associated with specific mailboxes or the
 server as a whole.  The server can choose to support only server
 annotations or both server and mailbox annotations.
 A server that supports both server and mailbox annotations indicates
 the presence of this extension by returning "METADATA" as one of the
 supported capabilities in the CAPABILITY command response.
 A server that supports only server annotations indicates the presence
 of this extension by returning "METADATA-SERVER" as one of the
 supported capabilities in the CAPABILITY command response.
 A server that supports unsolicited annotation change responses MUST
 support the "ENABLE" [RFC5161] extension to allow clients to turn
 that feature on.
 The METADATA extension adds two new commands and one new untagged
 response to the IMAP base protocol.
 This extension makes the following changes to the IMAP protocol:
 o  adds a new SETMETADATA command
 o  adds a new GETMETADATA command
 o  adds a new METADATA untagged response
 o  adds a new METADATA response code
 The rest of this document describes the data model and protocol
 changes more rigorously.

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", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].
 Whitespace and line breaks have been added to the examples in this
 document to promote readability.

Daboo Standards Track [Page 3] RFC 5464 The IMAP METADATA Extension February 2009

3. Data Model

3.1. Overview

 Mailboxes or the server as a whole may have zero or more annotations
 associated with them.  An annotation contains a uniquely named entry,
 which has a value.  Annotations can be added to mailboxes when a
 mailbox name is provided as the first argument to the SETMETADATA
 command, or to the server as a whole when the empty string is
 provided as the first argument to the command.
 For example, a general comment being added to a mailbox may have an
 entry name of "/comment" and a value of "Really useful mailbox".
 The protocol changes to IMAP described below allow a client to access
 or change the values of any annotation entry, assuming it has
 sufficient access rights to do so.

3.2. Namespace of Entries

 Each annotation is an entry that has a hierarchical name, with each
 component of the name separated by a slash ("/").  An entry name MUST
 NOT contain two consecutive "/" characters and MUST NOT end with a
 "/" character.
 The value of an entry is NIL (has no value), or a string or binary
 data of zero or more octets.  A string MAY contain multiple lines of
 text.  Clients MUST use the CRLF (0x0D 0x0A) character octet sequence
 to represent line ends in a multi-line string value.
 Entry names MUST NOT contain asterisk ("*") or percent ("%")
 characters and MUST NOT contain non-ASCII characters or characters
 with octet values in the range 0x00 to 0x19.  Invalid entry names
 result in a BAD response in any IMAP command in which they are used.
 Entry names are case-insensitive.
 Use of control or punctuation characters in entry names is strongly
 discouraged.
 This specification defines an initial set of entry names available
 for use with mailbox and server annotations.  In addition, an
 extension mechanism is described to allow additional names to be
 added for extensibility.
 The first component in entry names defines the scope of the
 annotation.  Currently, only the prefixes "/private" or "/shared" are
 defined.  These prefixes are used to indicate whether an annotation

Daboo Standards Track [Page 4] RFC 5464 The IMAP METADATA Extension February 2009

 is stored on a per-user basis ("/private") and not visible to other
 users, or whether an annotation is shared between authorized users
 ("/shared") with a single value that can be read and changed by
 authorized users with appropriate access.  See Section 3.3 for
 details.
 Entry names can have any number of components starting at 2, unless
 they fall under the vendor namespaces (i.e., have a /shared/vendor/
 <vendor-token> or /private/vendor/<vendor-token> prefix as described
 below), in which case they have at least 4 components.

3.2.1. Entry Names

 Entry names MUST be specified in a Standards Track or IESG-approved
 Experimental RFC, or fall under the vendor namespace.  See
 Section 6.1 for the registration template.

3.2.1.1. Server Entries

 These entries are set or retrieved when the mailbox name argument to
 the new SETMETADATA or GETMETADATA command is the empty string.
 /shared/comment
    Defines a comment or note that is associated with the server and
    that is shared with authorized users of the server.
 /shared/admin
    Indicates a method for contacting the server administrator.  The
    value MUST be a URI (e.g., a mailto: or tel: URL).  This entry is
    always read-only -- clients cannot change it.  It is visible to
    authorized users of the system.
 /shared/vendor/<vendor-token>
    Defines the top level of shared entries associated with the
    server, as created by a particular product of some vendor.  This
    entry can be used by vendors to provide server- or client-specific
    annotations.  The vendor-token MUST be registered with IANA, using
    the Application Configuration Access Protocol (ACAP) [RFC2244]
    vendor subtree registry.
 /private/vendor/<vendor-token>
    Defines the top level of private entries associated with the
    server, as created by a particular product of some vendor.  This
    entry can be used by vendors to provide server- or client-specific

Daboo Standards Track [Page 5] RFC 5464 The IMAP METADATA Extension February 2009

    annotations.  The vendor-token MUST be registered with IANA, using
    the ACAP [RFC2244] vendor subtree registry.

3.2.1.2. Mailbox Entries

 These entries are set or retrieved when the mailbox name argument to
 the new SETMETADATA or GETMETADATA command is not the empty string.
 /shared/comment
    Defines a shared comment or note associated with a mailbox.
 /private/comment
    Defines a private (per-user) comment or note associated with a
    mailbox.
 /shared/vendor/<vendor-token>
    Defines the top level of shared entries associated with a specific
    mailbox, as created by a particular product of some vendor.  This
    entry can be used by vendors to provide client-specific
    annotations.  The vendor-token MUST be registered with IANA, using
    the ACAP [RFC2244] vendor subtree registry.
 /private/vendor/<vendor-token>
    Defines the top level of private entries associated with a
    specific mailbox, as created by a particular product of some
    vendor.  This entry can be used by vendors to provide client-
    specific annotations.  The vendor-token MUST be registered with
    IANA, using the ACAP [RFC2244] vendor subtree registry.

3.3. Private versus Shared and Access Control

 In the absence of the ACL (Access Control List) extension [RFC4314],
 users can only set and retrieve private or shared mailbox annotations
 on a mailbox that exists and is returned to them via a LIST or LSUB
 command, and on which they have either read or write access to the
 actual message content of the mailbox (as determined by the READ-ONLY
 and READ-WRITE response codes as described in Section 5.2 of
 [RFC4314]).
 When the ACL extension [RFC4314] is present, users can only set and
 retrieve private or shared mailbox annotations on a mailbox on which
 they have the "l" right and any one of the "r", "s", "w", "i", or "p"
 rights.

Daboo Standards Track [Page 6] RFC 5464 The IMAP METADATA Extension February 2009

 If a client attempts to set or retrieve annotations on mailboxes that
 do not satisfy the conditions above, the server MUST respond with a
 NO response.
 Users can always retrieve private or shared server annotations if
 they exist.  Servers MAY restrict the creation of private or shared
 server annotations as appropriate.  When restricted, the server MUST
 return a NO response when the SETMETADATA command is used to try to
 create a server annotation.
 If the METADATA extension is present, support for shared annotations
 is REQUIRED, whilst support for private annotations is OPTIONAL.
 This recognizes the fact that support for private annotations may
 introduce significantly more complexity to a server in terms of
 tracking ownership of the annotations, how quota is determined for
 users based on their own annotations, etc.

4. IMAP Protocol Changes

4.1. General Considerations

 The new SETMETADATA command and the METADATA response each have a
 mailbox name argument.  An empty string is used for the mailbox name
 to signify server annotations.  A non-empty string is used to signify
 mailbox annotations attached to the corresponding mailbox.
 Servers SHOULD ensure that mailbox annotations are automatically
 moved when the mailbox they refer to is renamed, i.e., the
 annotations follow the mailbox.  This applies to a rename of the
 INBOX, with the additional behavior that the annotations are copied
 from the original INBOX to the renamed mailbox, i.e., mailbox
 annotations are preserved on the INBOX when it is renamed.
 Servers SHOULD delete annotations for a mailbox when the mailbox is
 deleted, so that a mailbox created with the same name as a previously
 existing mailbox does not inherit the old mailbox annotations.
 Servers SHOULD allow annotations on all 'types' of mailboxes,
 including ones reporting \Noselect for their LIST response.  Servers
 can implicitly remove \Noselect mailboxes when all child mailboxes
 are removed, and, at that time any annotations associated with the
 \Noselect mailbox SHOULD be removed.
 The server is allowed to impose limitations on the size of any one
 annotation or the total number of annotations for a single mailbox or
 for the server as a whole.  However, the server MUST accept an
 annotation data size of at least 1024 bytes, and an annotation count
 per server or mailbox of at least 10.

Daboo Standards Track [Page 7] RFC 5464 The IMAP METADATA Extension February 2009

 Some annotations may be "read-only" -- i.e., they are set by the
 server and cannot be changed by the client.  Also, such annotations
 may be "computed" -- i.e., the value changes based on underlying
 properties of the mailbox or server.  For example, an annotation
 reporting the total size of all messages in the mailbox would change
 as messages are added or removed.  Or, an annotation containing an
 IMAP URL for the mailbox would change if the mailbox was renamed.
 Servers MAY support sending unsolicited responses for use when
 annotations are changed by some "third-party" (see Section 4.4).  In
 order to do so, servers MUST support the ENABLE command [RFC5161] and
 MUST only send unsolicited responses if the client used the ENABLE
 command [RFC5161] extension with the capability string "METADATA" or
 "METADATA-SERVER" earlier in the session, depending on which of those
 capabilities is supported by the server.

4.2. GETMETADATA Command

 This extension adds the GETMETADATA command.  This allows clients to
 retrieve server or mailbox annotations.
 This command is only available in authenticated or selected state
 [RFC3501].
     Arguments:  mailbox-name
                 options
                 entry-specifier
     Responses:  required METADATA response
     Result:     OK - command completed
                 NO - command failure: can't access annotations on
                      the server
                 BAD - command unknown or arguments invalid
 When the mailbox name is the empty string, this command retrieves
 server annotations.  When the mailbox name is not empty, this command
 retrieves annotations on the specified mailbox.
 Options MAY be included with this command and are defined below.
 Example:
         C: a GETMETADATA "" /shared/comment
         S: * METADATA "" (/shared/comment "Shared comment")
         S: a OK GETMETADATA complete

Daboo Standards Track [Page 8] RFC 5464 The IMAP METADATA Extension February 2009

    In the above example, the contents of the value of the "/shared/
    comment" server entry is requested by the client and returned by
    the server.
 Example:
         C: a GETMETADATA "INBOX" /private/comment
         S: * METADATA "INBOX" (/private/comment "My own comment")
         S: a OK GETMETADATA complete
    In the above example, the contents of the value of the "/private/
    comment" mailbox entry for the mailbox "INBOX" is requested by the
    client and returned by the server.
 Entry specifiers can be lists of atomic specifiers, so that multiple
 annotations may be returned in a single GETMETADATA command.
 Example:
         C: a GETMETADATA "INBOX" (/shared/comment /private/comment)
         S: * METADATA "INBOX" (/shared/comment "Shared comment"
                                /private/comment "My own comment")
         S: a OK GETMETADATA complete
    In the above example, the values of the two server entries
    "/shared/comment" and "/private/comment" on the mailbox "INBOX"
    are requested by the client and returned by the server.

4.2.1. MAXSIZE GETMETADATA Command Option

 When the MAXSIZE option is specified with the GETMETADATA command, it
 restricts which entry values are returned by the server.  Only entry
 values that are less than or equal in octet size to the specified
 MAXSIZE limit are returned.  If there are any entries with values
 larger than the MAXSIZE limit, the server MUST include the METADATA
 LONGENTRIES response code in the tagged OK response for the
 GETMETADATA command.  The METADATA LONGENTRIES response code returns
 the size of the biggest entry value requested by the client that
 exceeded the MAXSIZE limit.
 Example:
         C: a GETMETADATA "INBOX" (MAXSIZE 1024)
                                  (/shared/comment /private/comment)
         S: * METADATA "INBOX" (/private/comment "My own comment")
         S: a OK [METADATA LONGENTRIES 2199] GETMETADATA complete

Daboo Standards Track [Page 9] RFC 5464 The IMAP METADATA Extension February 2009

    In the above example, the values of the two server entries
    "/shared/comment" and "/private/comment" on the mailbox "INBOX"
    are requested by the client, which wants to restrict the size of
    returned values to 1024 octets.  In this case, the "/shared/
    comment" entry value is 2199 octets and is not returned.

4.2.2. DEPTH GETMETADATA Command Option

 When the DEPTH option is specified with the GETMETADATA command, it
 extends the list of entry values returned by the server.  For each
 entry name specified in the GETMETADATA command, the server returns
 the value of the specified entry name (if it exists), plus all
 entries below the entry name up to the specified DEPTH.  Three values
 are allowed for DEPTH:
 "0" - no entries below the specified entry are returned
 "1" - only entries immediately below the specified entry are returned
 "infinity" -  all entries below the specified entry are returned
 Thus, "depth 1" for an entry "/a" will match "/a" as well as its
 children entries (e.g., "/a/b"), but will not match grandchildren
 entries (e.g., "/a/b/c").
 If the DEPTH option is not specified, this is the same as specifying
 "DEPTH 0".
 Example:
         C: a GETMETADATA "INBOX" (DEPTH 1)
                                 (/private/filters/values)
         S: * METADATA "INBOX" (/private/filters/values/small
              "SMALLER 5000" /private/filters/values/boss
              "FROM \"boss@example.com\"")
         S: a OK GETMETADATA complete
    In the above example, 2 entries below the /private/filters/values
    entry exist on the mailbox "INBOX": "/private/filters/values/
    small" and "/private/filters/values/boss".

4.3. SETMETADATA Command

 This extension adds the SETMETADATA command.  This allows clients to
 set annotations.
 This command is only available in authenticated or selected state
 [RFC3501].

Daboo Standards Track [Page 10] RFC 5464 The IMAP METADATA Extension February 2009

     Arguments:  mailbox-name
                 entry
                 value
                 list of entry, values
     Responses:  no specific responses for this command
     Result:     OK - command completed
                 NO - command failure: can't set annotations,
                      or annotation too big or too many
                 BAD - command unknown or arguments invalid
 This command sets the specified list of entries by adding or
 replacing the specified values provided, on the specified existing
 mailboxes or on the server (if the mailbox argument is the empty
 string).  Clients can use NIL for the value of entries it wants to
 remove.  The server SHOULD NOT return a METADATA response containing
 the updated annotation data.  Clients MUST NOT assume that a METADATA
 response will be sent, and MUST assume that if the command succeeds,
 then the annotation has been changed.
 If the server is unable to set an annotation because the size of its
 value is too large, the server MUST return a tagged NO response with
 a "[METADATA MAXSIZE NNN]" response code when NNN is the maximum
 octet count that it is willing to accept.
 If the server is unable to set a new annotation because the maximum
 number of allowed annotations has already been reached, the server
 MUST return a tagged NO response with a "[METADATA TOOMANY]" response
 code.
 If the server is unable to set a new annotation because it does not
 support private annotations on one of the specified mailboxes, the
 server MUST return a tagged NO response with a "[METADATA NOPRIVATE]"
 response code.
 When any one annotation fails to be set, resulting in a tagged NO
 response from the server, then the server MUST NOT change the values
 for other annotations specified in the SETMETADATA command.
 Example:
         C: a SETMETADATA INBOX (/private/comment {33}
         S: + ready for data
         My new comment across
         two lines.
         )
         S: a OK SETMETADATA complete

Daboo Standards Track [Page 11] RFC 5464 The IMAP METADATA Extension February 2009

    In the above example, the entry "/private/comment" for the mailbox
    "INBOX" is created (if not already present) and the value set to a
    multi-line string.
 Example:
         C: a SETMETADATA INBOX (/private/comment NIL)
         S: a OK SETMETADATA complete
    In the above example, the entry "/private/comment" is removed from
    the mailbox "INBOX".
 Multiple entries can be set in a single SETMETADATA command by
 listing entry-value pairs in the list.
 Example:
         C: a SETMETADATA INBOX (/private/comment "My new comment"
                             /shared/comment "This one is for you!")
         S: a OK SETMETADATA complete
    In the above example, the entries "/private/comment" and "/shared/
    comment" for the mailbox "INBOX" are created (if not already
    present) and the values set as specified.
 Example:
         C: a SETMETADATA INBOX (/private/comment "My new comment")
         S: a NO [METADATA TOOMANY] SETMETADATA failed
    In the above example, the server is unable to set the requested
    (new) annotation as it has reached the limit on the number of
    annotations it can support on the specified mailbox.

4.4. METADATA Response

 The METADATA response displays results of a GETMETADATA command, or
 can be returned as an unsolicited response at any time by the server
 in response to a change in a server or mailbox annotation.
 When unsolicited responses are activated by the ENABLE [RFC5161]
 command for this extension, servers MUST send unsolicited METADATA
 responses if server or mailbox annotations are changed by a third-
 party, allowing servers to keep clients updated with changes.
 Unsolicited METADATA responses MUST only contain entry names, not the
 values.  If the client wants to update any cached values, it must
 explicitly retrieve those using a GETMETADATA command.

Daboo Standards Track [Page 12] RFC 5464 The IMAP METADATA Extension February 2009

 The METADATA response can contain multiple entries in a single
 response, but the server is free to return multiple responses for
 each entry or group of entries, if it desires.
 This response is only available in authenticated or selected state
 [RFC3501].

4.4.1. METADATA Response with Values

 The response consists of a list of entry-value pairs.
 Example:
         C: a GETMETADATA "" /shared/comment
         S: * METADATA "" (/shared/comment "My comment")
         S: a OK GETMETADATA complete
    In the above example, a single entry with its value is returned by
    the server.
 Example:
         C: a GETMETADATA "INBOX" /private/comment /shared/comment
         S: * METADATA "INBOX" (/private/comment "My comment"
                                /shared/comment "Its sunny outside!")
         S: a OK GETMETADATA complete
    In the above example, two entries and their values are returned by
    the server.
 Example:
         C: a GETMETADATA "INBOX" /private/comment /shared/comment
         S: * METADATA "INBOX" (/private/comment "My comment")
         S: * METADATA "INBOX" (/shared/comment "Its sunny outside!")
         S: a OK GETMETADATA complete
    In the above example, the server returns two separate responses
    for each of the two entries requested.

4.4.2. Unsolicited METADATA Response without Values

 The response consists of a list of entries, each of which have
 changed on the server or mailbox.
 Example:

Daboo Standards Track [Page 13] RFC 5464 The IMAP METADATA Extension February 2009

         C: a NOOP
         S: * METADATA "" /shared/comment
         S: a OK NOOP complete
    In the above example, the server indicates that the "/shared/
    comment" server entry has been changed.
 Example:
         C: a NOOP
         S: * METADATA "INBOX" /shared/comment /private/comment
         S: a OK NOOP complete
    In the above example, the server indicates a change to two mailbox
    entries.

5. Formal Syntax

 The following syntax specification uses the Augmented Backus-Naur
 Form (ABNF) notation as specified in [RFC5234].
 Non-terminals referenced but not defined below are as defined by
 [RFC3501], with the new definitions in [RFC4466] superseding those in
 [RFC3501].
 Except as noted otherwise, all alphabetic characters are case-
 insensitive.  The use of upper or lower case characters to define
 token strings is for editorial clarity only.  Implementations MUST
 accept these strings in a case-insensitive fashion.
    capability        =/ "METADATA" / "METADATA-SERVER"
                        ; defines the capabilities for this extension.
    command-auth      =/ setmetadata / getmetadata
                        ; adds to original IMAP command
    entries           = entry /
                        "(" entry *(SP entry) ")"
                        ; entry specifiers
    entry             = astring
                        ; slash-separated path to entry
                        ; MUST NOT contain "*" or "%"
    entry-value       = entry SP value
    entry-values      = "(" entry-value *(SP entry-value) ")"

Daboo Standards Track [Page 14] RFC 5464 The IMAP METADATA Extension February 2009

    entry-list        = entry *(SP entry)
                        ; list of entries used in unsolicited
                        ; METADATA response
    getmetadata       = "GETMETADATA" [SP getmetadata-options]
                                      SP mailbox SP entries
                        ; empty string for mailbox implies
                        ; server annotation.
    getmetadata-options = "(" getmetadata-option
                              *(SP getmetadata-option) ")"
    getmetadata-option = tagged-ext-label [SP tagged-ext-val]
                        ; tagged-ext-label and tagged-ext-val
                        ; are defined in [RFC4466].
    maxsize-opt       = "MAXSIZE" SP number
                        ; Used as a getmetadata-option
    metadata-resp     = "METADATA" SP mailbox SP
                        (entry-values / entry-list)
                        ; empty string for mailbox implies
                        ; server annotation.
    response-payload  =/ metadata-resp
                        ; adds to original IMAP data responses
    resp-text-code    =/ "METADATA" SP "LONGENTRIES" SP number
                           ; new response codes for GETMETADATA
    resp-text-code    =/ "METADATA" SP ("MAXSIZE" SP number /
                                        "TOOMANY" / "NOPRIVATE")
                        ; new response codes for SETMETADATA
                        ; failures
    scope-opt         =  "DEPTH" SP ("0" / "1" / "infinity")
                        ; Used as a getmetadata-option
    setmetadata       = "SETMETADATA" SP mailbox
                                      SP entry-values
                        ; empty string for mailbox implies
                        ; server annotation.
    value             = nstring / literal8

Daboo Standards Track [Page 15] RFC 5464 The IMAP METADATA Extension February 2009

6. IANA Considerations

 All entries MUST have either "/shared" or "/private" as a prefix.
 Entry names MUST be specified in a Standards Track or IESG-approved
 Experimental RFC, or fall under the vendor namespace (i.e., use
 /shared/vendor/<vendor-token> or /private/vendor/<vendor-token> as
 the prefix).
 Each entry registration MUST include a content-type that is used to
 indicate the nature of the annotation value.  Where applicable, a
 charset parameter MUST be included with the content-type.

6.1. Entry and Attribute Registration Template

     To: iana@iana.org
     Subject: IMAP METADATA Entry Registration
     Type:         [Either "Mailbox" or "Server"]
     Name:         [the name of the entry]
     Description:  [a description of what the entry is for]
     Content-type: [MIME Content-Type and charset for the entry value]
     RFC Number:   [for entries published as RFCs]
     Contact:      [email and/or physical address to contact for
                    additional information]

6.2. Server Entry Registrations

 The following templates specify the IANA registrations of annotation
 entries specified in this document.

Daboo Standards Track [Page 16] RFC 5464 The IMAP METADATA Extension February 2009

6.2.1. /shared/comment

     To: iana@iana.org
     Subject: IMAP METADATA Entry Registration
     Type:         Server
     Name:         /shared/comment
     Description:  Defines a comment or note that is associated
                   with the server and that is shared with
                   authorized users of the server.
     Content-type: text/plain; charset=utf-8
     RFC Number:   RFC 5464
     Contact:      IMAP Extensions mailto:ietf-imapext@imc.org

6.2.2. /shared/admin

   To: iana@iana.org
   Subject: IMAP METADATA Entry Registration
   Type:         Server
   Name:         /shared/admin
   Description:  Indicates a method for contacting the server
                 administrator.  The value MUST be a URI (e.g., a
                 mailto: or tel: URL).  This entry is always
                 read-only -- clients cannot change it.  It is visible
                 to authorized users of the system.
   Content-type: text/plain; charset=utf-8
   RFC Number:   RFC 5464
   Contact:      IMAP Extensions mailto:ietf-imapext@imc.org

6.3. Mailbox Entry Registrations

 The following templates specify the IANA registrations of annotation
 entries specified in this document.

Daboo Standards Track [Page 17] RFC 5464 The IMAP METADATA Extension February 2009

6.3.1. /shared/comment

     To: iana@iana.org
     Subject: IMAP METADATA Entry Registration
     Type:         Mailbox
     Name:         /shared/comment
     Description:  Defines a shared comment or note associated with a
                   mailbox.
     Content-type: text/plain; charset=utf-8
     RFC Number:   RFC 5464
     Contact:      IMAP Extensions mailto:ietf-imapext@imc.org

6.3.2. /private/comment

     To: iana@iana.org
     Subject: IMAP METADATA Entry Registration
     Type:         Mailbox
     Name:         /private/comment
     Description:  Defines a private comment or note associated with a
                   mailbox.
     Content-type: text/plain; charset=utf-8
     RFC Number:   RFC 5464
     Contact:      IMAP Extensions mailto:ietf-imapext@imc.org

7. Security Considerations

 The security considerations in Section 11 of [RFC3501] apply here
 with respect to protecting annotations from snooping.  Servers MAY
 choose to only support the METADATA and/or METADATA-SERVER extensions
 after a privacy layer has been negotiated by the client.
 Annotations can contain arbitrary data of varying size.  As such,
 servers MUST ensure that size limits are enforced to prevent a user
 from using up all available space on a server and preventing use by
 others.  Clients MUST treat annotation data values as an "untrusted"
 source of data as it is possible for it to contain malicious content.

Daboo Standards Track [Page 18] RFC 5464 The IMAP METADATA Extension February 2009

 Annotations whose values are intended to remain private MUST be
 stored only in entries that have the "/private" prefix on the entry
 name.
 Excluding the above issues, the METADATA extension does not raise any
 security considerations that are not present in the base IMAP
 protocol, and these issues are discussed in [RFC3501].

8. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2244]  Newman, C. and J. Myers, "ACAP -- Application
            Configuration Access Protocol", RFC 2244, November 1997.
 [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
            4rev1", RFC 3501, March 2003.
 [RFC4314]  Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
            RFC 4314, December 2005.
 [RFC4466]  Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4
            ABNF", RFC 4466, April 2006.
 [RFC5161]  Gulbrandsen, A. and A. Melnikov, "The IMAP ENABLE
            Extension", RFC 5161, March 2008.
 [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
            Specifications: ABNF", STD 68, RFC 5234, January 2008.

Appendix A. Acknowledgments

 The ideas expressed in this document are based on the message
 annotation document that was co-authored by Randall Gellens.  The
 author would like to thank the following individuals for contributing
 their ideas and support for writing this specification: Dave
 Cridland, Arnt Gulbrandsen, Dan Karp, Alexey Melnikov, Ken Murchison,
 Chris Newman, and Michael Wener.

Daboo Standards Track [Page 19] RFC 5464 The IMAP METADATA Extension February 2009

Author's Address

 Cyrus Daboo
 Apple Inc.
 1 Infinite Loop
 Cupertino, CA  95014
 USA
 EMail: cyrus@daboo.name
 URI:   http://www.apple.com/

Daboo Standards Track [Page 20] RFC 5464 The IMAP METADATA Extension February 2009

Full Copyright Statement

 Copyright (C) The IETF Trust (2009).
 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 WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
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 attempt made to obtain a general license or permission for the use of
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Daboo Standards Track [Page 21]

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