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RFC 5257 - Internet Message Access Protocol - ANNOTATE Extension


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Network Working Group                                           C. Daboo
Request for Comments: 5257                                    Apple Inc.
Category: Experimental                                        R. Gellens
                                                   QUALCOMM Incorporated
                                                               June 2008

         Internet Message Access Protocol - ANNOTATE Extension

Status of This Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Abstract

   The ANNOTATE extension to the Internet Message Access Protocol
   permits clients and servers to maintain "meta data" for messages, or
   individual message parts, stored in a mailbox on the server.  For
   example, this can be used to attach comments and other useful
   information to a message.  It is also possible to attach annotations
   to specific parts of a message, so that, for example, they could be
   marked as seen, or important, or a comment added.

   Note that this document was the product of a WG that had good
   consensus on how to approach the problem.  Nevertheless, the WG felt
   it did not have enough information on implementation and deployment
   hurdles to meet all of the requirements of a Proposed Standard.  The
   IETF solicits implementations and implementation reports in order to
   make further progress.

   Implementers should be aware that this specification may change in an
   incompatible manner when going to Proposed Standard status.  However,
   any incompatible changes will result in a new capability name being
   used to prevent problems with any deployments of the experimental
   extension.

Table of Contents

   1. Introduction and Overview .......................................3
   2. Conventions Used in This Document ...............................4
   3. Data Model ......................................................4
      3.1. Overview ...................................................4
      3.2. Namespace of Entries and Attributes ........................4
           3.2.1. Entry Names .........................................5
           3.2.2. Attribute Names .....................................7
      3.3. Private Versus Shared ......................................7
      3.4. Access Control .............................................8
      3.5. Access to Standard IMAP Flags and Keywords ................11
   4. IMAP Protocol Changes ..........................................11
      4.1. General Considerations ....................................11
      4.2. ANNOTATE Parameter with the SELECT/EXAMINE Commands .......12
      4.3. ANNOTATION Message Data Item in FETCH Command .............12
      4.4. ANNOTATION Message Data Item in FETCH Response ............14
      4.5. ANNOTATION Message Data Item in STORE .....................16
      4.6. ANNOTATION Interaction with COPY ..........................18
      4.7. ANNOTATION Message Data Item in APPEND ....................18
      4.8. ANNOTATION Criterion in SEARCH ............................19
      4.9. ANNOTATION Key in SORT ....................................20
      4.10. New ACL Rights ...........................................21
   5. Formal Syntax ..................................................21
   6. IANA Considerations ............................................23
      6.1. Entry and Attribute Registration Template .................23
      6.2. Entry Registrations .......................................24
           6.2.1. /comment ...........................................24
           6.2.2. /flags .............................................24
           6.2.3. /altsubject ........................................25
           6.2.4. /<section-part>/comment ............................25
           6.2.5. /<section-part>/flags/seen .........................26
           6.2.6. /<section-part>/flags/answered .....................26
           6.2.7. /<section-part>/flags/flagged ......................27
           6.2.8. /<section-part>/flags/forwarded ....................27
      6.3. Attribute Registrations ...................................28
           6.3.1. value ..............................................28
           6.3.2. size ...............................................28
      6.4. Capability Registration ...................................28
   7. Internationalization Considerations ............................29
   8. Security Considerations ........................................29
   9. References .....................................................29
      9.1. Normative References ......................................29
      9.2. Informative References ....................................30
   10. Acknowledgments ...............................................30

1.  Introduction and Overview

   The ANNOTATE extension is present in any IMAP [RFC3501]
   implementation that returns "ANNOTATE-EXPERIMENT-1" as one of the
   supported capabilities in the CAPABILITY response.

   This extension makes the following changes to the IMAP protocol:

     a.  adds a new ANNOTATION message data item for use in FETCH.

     b.  adds a new ANNOTATION message data item for use in STORE.

     c.  adds a new ANNOTATION search criterion for use in SEARCH.

     d.  adds a new ANNOTATION sort key for use in the SORT extension.

     e.  adds a new ANNOTATION data item for use in APPEND.

     f.  adds a new requirement on the COPY command.

     g.  adds a new ANNOTATE parameter for use with the SELECT/EXAMINE
         commands.

     h.  adds two new response codes to indicate store failures of
         annotations.

     i.  adds a new untagged response code for the SELECT or EXAMINE
         commands to indicate the maximum sized annotation that can be
         stored.

     j.  adds a new Access Control List (ACL) "bit" for use with the ACL
         extensions [RFC2086] and [RFC4314].

   The data model used for the storage of annotations is based on the
   Application Configuration Access Protocol [RFC2244].  Note that there
   is no inheritance in annotations.

   If a server supports annotations, then it MUST store all annotation
   data permanently, i.e., there is no concept of "session only"
   annotations that would correspond to the behavior of "session" flags
   as defined in the IMAP base specification.

   In order to provide optimum support for a disconnected client (one
   that needs to synchronize annotations for use when offline), servers
   SHOULD also support the Conditional STORE [RFC4551] extension.

   The rest of this document describes the data model and protocol
   changes more rigorously.

2.  Conventions Used in This Document

   The examples in this document use "C:" and "S:" to 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].

3.  Data Model

3.1.  Overview

   The data model for annotations in ANNOTATE uses a uniquely named
   entry that contains a set of standard attributes.  Thus, a single
   coherent unit of "meta data" for a message is stored as a single
   entry, made up of several attributes.

   For example, a comment annotation added to a message has an entry
   name of "/comment".  This entry is composed of several attributes
   such as "value", "size", etc., that contain the properties and data
   of the entry.

   The protocol changes to IMAP, described below, allow a client to
   access or change the values of any attribute in any entry in a
   message annotation, assuming it has sufficient access rights to do so
   (see Section 3.4 for specifics).

3.2.  Namespace of Entries and Attributes

   A message may contain zero or more annotations, each of which is a
   single uniquely named entry.  Each entry 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.

   Each entry is made up of a set of attributes.  Each attribute has a
   hierarchical name, with each component of the name separated by a
   period (".").  An attribute name MUST NOT contain two consecutive "."
   characters and MUST NOT end with a "." character.

   The value of an attribute is "NIL" (has no value), or is a string of
   zero or more octets.

   Entry and attribute names MUST NOT contain asterisk ("*") or percent
   ("%") characters, and MUST NOT contain non-ASCII characters or the
   NULL octet.  Invalid entry or attribute names result in a BAD
   response in any IMAP commands where they are used.

   Attribute names MUST NOT contain any hierarchical components with the
   names "priv" or "shared", as those have special meaning (see Section
   3.3).

   Entry and attribute names are case-sensitive.

   Use of control or punctuation characters in entry and attribute names
   is strongly discouraged.

   This specification defines an initial set of entry and attribute
   names available for use in message annotations.  In addition, an
   extension mechanism is described to allow additional names to be
   added as needed.

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.

   /
      Defines the top-level of entries associated with an entire
      message.  This entry itself does not contain any attributes.  All
      entries that start with a numeric character ("0" - "9") refer to
      an annotation on a specific body part.  All other entries are for
      annotations on the entire message.

   /comment
      Defines a comment or note associated with an entire message.

   /flags
      This entry hierarchy is reserved for future use.

   /altsubject
      Contains text supplied by the message recipient to be used by the
      client, instead of the original message Subject.

   /vendor/<vendor-token>
      Defines the top-level of entries associated with an entire message
      as created by a particular product of some vendor.  These sub-
      entries can be used by vendors to provide client-specific
      annotations.  The vendor-token MUST be registered with IANA, using
      the [RFC2244] vendor subtree registry.

   /<section-part>
      Defines the top-level of entries associated with a specific body
      part of a message.  This entry itself does not contain any
      attributes.  The section-part is a numeric part specifier.  Its

      syntax is the same as the section-part ABNF element defined in
      [RFC3501].  The server MUST return a BAD response if the client
      uses an incorrect part specifier (either incorrect syntax or a
      specifier referring to a non-existent part).  The server MUST
      return a BAD response if the client uses an empty part specifier
      (which is used in IMAP to represent the entire message).

   /<section-part>/comment
      Defines a comment or note associated with a specific body part of
      a message.

   /<section-part>/flags
      Defines the top-level of entries associated with the flag state
      for a specific body part of a message.  All sub-entries are
      maintained entirely by the client.  There is no implicit change to
      any flag by the server.

          /<section-part>/flags/seen
             This is similar to the IMAP \Seen flag, except it applies
             to only the body part referenced by the entry.

          /<section-part>/flags/answered
             This is similar to the IMAP \Answered flag, except it
             applies to only the body part referenced by the entry.

          /<section-part>/flags/flagged
             This is similar to the IMAP \Flagged flag, except it
             applies to only the body part referenced by the entry.

          /<section-part>/flags/forwarded
             This is similar to the IMAP $Forwarded keyword, except it
             applies to only the body part referenced by the entry.

      Defines flags for a specific body part of a message.  The "value"
      attribute of each of the entries described above must be either
      "1", "0", or "NIL".  "1" corresponds to the flag being set.

   /<section-part>/vendor/<vendor-token>
      Defines the top-level of entries associated with a specific body
      part of a message 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.

3.2.2.  Attribute Names

   Attribute names MUST be specified in a standards track or IESG
   approved experimental RFC.  See Section 6.1 for the registration
   template.

   All attribute names implicitly have a ".priv" and a ".shared" suffix
   that maps to private and shared versions of the entry.  Searching or
   fetching without using either suffix will include both.  The client
   MUST specify either a ".priv" or ".shared" suffix when storing an
   annotation or sorting on annotations.

   value
      A string or binary data representing the value of the annotation.
      To delete an annotation, the client can store "NIL" into the
      value.  If the client requests the value attribute for a non-
      existent entry, then the server MUST return "NIL" for the value.
      The content represented by the string is determined by the
      content-type used to register the entry (see Section 6.1 for entry
      registration templates).  Where applicable, the registered
      content-type MUST include a charset parameter.  Text values SHOULD
      use the utf-8 [RFC3629] character set.  Note that binary data
      (data which may contain the NULL octet) is allowed (e.g., for
      storing images), and this extension uses the "literal8" syntax
      element [RFC4466] to allow such data to be written to or read from
      the server.

   size
      The size of the value, in octets.  Set automatically by the
      server, read-only to clients.  If the client requests the size
      attribute for a non-existent entry, then the server MUST return
      "0" (zero) for the size.

3.3.  Private Versus Shared

   Some IMAP mailboxes are private, accessible only to the owning user.
   Other mailboxes are not, either because the owner has set an ACL
   [RFC4314] that permits access by other users, or because it is a
   shared mailbox.

   This raises the issue of shared versus private annotations.

   If all annotations are private, it is then impossible to have
   annotations in a shared or otherwise non-private mailbox be visible
   to other users.  This eliminates what could be a useful aspect of
   annotations in a shared environment.  An example of such use is a
   shared IMAP folder containing bug reports.  Engineers may want to use

   annotations to add information to existing messages, indicate
   assignments, status, etc.  This use requires shared annotations.

   If all annotations are shared, it is impossible to use annotations
   for private notes on messages in shared mailboxes.  Also, modifying
   an ACL to permit access to a mailbox by other users may
   unintentionally expose private information.

   There are also situations in which both shared and private
   annotations are useful.  For example, an administrator may want to
   set shared annotations on messages in a shared folder, which
   individual users may wish to supplement with additional notes.

   If shared and private annotations are to coexist, we need a clear way
   to differentiate them.  Also, it should be as easy as possible for a
   client to access both and not overlook either.  There is also a
   danger in allowing a client to store an annotation without knowing if
   it is shared or private.

   This document proposes two standard suffixes for all attributes:
   ".shared" and ".priv".  A SEARCH or FETCH command that specifies
   neither, uses both.  STORE, APPEND, and SORT commands MUST explicitly
   use ".priv" or ".shared" suffixes.

   If the ANNOTATE extension is present, support for shared annotations
   in servers is REQUIRED, while support for private annotations in
   servers is OPTIONAL.  This recognizes the fact that support for
   private annotations may introduce a significant increase in
   complexity to a server in terms of tracking ownership of the
   annotations, how quota is determined for users based on their own
   annotations, etc.  Clients that support the ANNOTATE extension MUST
   handle both shared and private annotations.

3.4.  Access Control

   A user needs to have appropriate rights in order to read or write
   ".priv" or ".shared" annotation values.  How those rights are
   calculated depends on whether or not the ACL [RFC2086] extension or
   its update [RFC4314] is present.  If a client attempts to store or
   fetch an annotation to which they do not have the appropriate rights,
   the server MUST respond with a NO response.

   When the ACL extension is not present, access to annotation values is
   governed by the nature of the selected state, in particular whether
   the mailbox was SELECTED or EXAMINED in READ-ONLY or READ-WRITE mode.

   When the ACL extension is present, the server MUST recognize the new
   ACL "n" right, in addition to the ones defined by the ACL extension
   itself.

   For ".priv" annotation values, the "r" right controls both read and
   write access.  When it is on, access to ".priv" annotations is
   allowed; when it is off, access to ".priv" annotations is disallowed.

   For ".shared" annotation values, the "r" right controls read access.
   When it is on, ".shared" annotations can be read; when it is off,
   ".shared" annotations cannot be read.

   For ".shared" annotation values, the "n" right controls write access.
   When it is on, ".shared" annotations can be changed or created
   through either a STORE or APPEND command; when it is off, ".shared"
   annotations cannot be changed or created.  The "n" right constitutes
   a "shared flag right" as defined in Section 6.2 of [RFC4314].

   A summary of all the access control restrictions is tabulated below

   +---------------+---------------+-----------------------------------+
   |  Server Type  | Action on     | Type of mailbox                   |
   |               | annotation    |                                   |
   +===============+===============+===================================+
   |               |               |                                   |
   |               | read .priv    | Any mailbox that can be SELECTED  |
   |               | values        | or EXAMINED.                      |
   |               |               |                                   |
   |               +---------------+-----------------------------------+
   |               |               |                                   |
   |               | write .priv   | Any SELECTED [READ-WRITE] mailbox.|
   |               | values        | SELECTED [READ-ONLY] mailboxes MAY|
   | Server        |               | also permit writes.               |
   | without       |               |                                   |
   | ACL Extension +---------------+-----------------------------------+
   |               |               |                                   |
   |               | read .shared  | Any mailbox that can be SELECTED  |
   |               | values        | or EXAMINED.                      |
   |               |               |                                   |
   |               +---------------+-----------------------------------+
   |               |               |                                   |
   |               | write .shared | Any mailbox that can be SELECTED  |
   |               | values        | or EXAMINED and is [READ-WRITE].  |
   |               |               |                                   |
   +---------------+---------------+-----------------------------------+
   |               |               |                                   |
   |               | read .priv    | Any mailbox with the "r"          |
   |               | values        | ACL right.                        |
   |               |               |                                   |
   |               +---------------+-----------------------------------+
   |               |               |                                   |
   |               | write .priv   | Any mailbox with the "r"          |
   | Server        | values        | ACL right.                        |
   | with          |               |                                   |
   | ACL Extension +---------------+-----------------------------------+
   |               |               |                                   |
   |               | read .shared  | Any mailbox with the "r"          |
   |               | values        | ACL right.                        |
   |               |               |                                   |
   |               +---------------+-----------------------------------+
   |               |               |                                   |
   |               | write .shared | Any mailbox with the "n"          |
   |               | values        | ACL right.                        |
   |               |               |                                   |
   +---------------+---------------+-----------------------------------+

3.5.  Access to Standard IMAP Flags and Keywords

   Due to the ambiguity of how private and shared values would map to
   the base IMAP flag and keyword values, the ANNOTATE extension does
   not expose IMAP flags or keywords as entries.  However, the /flags
   annotation entry is reserved for future use and MUST NOT be used by
   clients or servers supporting this extension.

   Clients that need to implement shared and private "flags" can create
   their own annotation entries for those, completely bypassing the base
   IMAP flag/keyword behavior.

4.  IMAP Protocol Changes

4.1.  General Considerations

   Servers may be able to offer only a limited level of support for
   annotations in mailboxes, and it is useful for clients to be able to
   know what level of support is available.  Servers MUST return an
   ANNOTATIONS response code during the SELECT or EXAMINE command for a
   mailbox to indicate the level of support.  Possible data items used
   with the ANNOTATIONS response code are:

      "NONE" - this indicates that the mailbox being selected does not
      support annotations at all.  Clients MUST NOT attempt to use
      annotation extensions in commands for this mailbox.

      "READ-ONLY" - this indicates that the annotations supported by the
      mailbox cannot be changed by the client.  Clients MUST NOT attempt
      to store annotations on any messages in a mailbox with this
      response code.

      "NOPRIVATE" - this indicates that the server does not support
      private annotations on the mailbox.  Only shared annotations are
      supported.  Clients SHOULD only attempt to read or store
      annotations attributes with the ".shared" suffix.  If a client
      uses an attribute with the ".priv" suffix in a FETCH command, then
      servers should return the attribute value in the FETCH response as
      "NIL".  If a client uses an attribute with the ".priv" suffix in a
      STORE command (or an APPEND command targeted at the mailbox), then
      the server MUST return a NO response.

      numeric values - if servers support writable annotations, then the
      server MUST indicate the maximum size in octets for an annotation
      value by providing the maximum size value in the response code.
      Clients MUST NOT store annotation values of a size greater than
      the amount indicated by the server.  Servers MUST accept a minimum

      annotation data size of at least 1024 octets if annotations can be
      written.

   In addition, the server MAY limit the total number of annotations for
   a single message.  However, the server MUST provide a minimum
   annotation count per message of at least 10.

4.2.  ANNOTATE Parameter with the SELECT/EXAMINE Commands

   The ANNOTATE extension defines a single optional SELECT parameter
   [RFC4466] "ANNOTATE", which is used to turn on unsolicited responses
   for annotations as described in Section 4.4.  This optional parameter
   results in a per-mailbox state change, i.e., it must be used in each
   SELECT/EXAMINE command in order to be effective, irrespective of
   whether it was used in a previous SELECT/EXAMINE during the same
   session.

   Example:

         C: a SELECT INBOX (ANNOTATE)
         S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen)
         S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft
                                           \Deleted \Seen \*)]
         S: * 10268 EXISTS
         S: * 1 RECENT
         S: * OK [UNSEEN 10268]
         S: * OK [UIDVALIDITY 890061587]
         S: * OK [UIDNEXT 34643]
         S: * OK [ANNOTATIONS 20480 NOPRIVATE]
         S: a OK [READ-WRITE] Completed

      In the above example, a SELECT command with the ANNOTATE parameter
      is issued.  The response from the server includes the required
      ANNOTATIONS response that indicates that the server supports
      annotations up to a maximum size of 20480 octets, and does not
      support private annotations (only shared).

4.3.  ANNOTATION Message Data Item in FETCH Command

   This extension adds an ANNOTATION message data item to the FETCH
   command.  This allows clients to retrieve annotations for a range of
   messages in the currently selected mailbox.

   ANNOTATION <entry-specifier> <attribute-specifier>

      The ANNOTATION message data item, when used by the client in the
      FETCH command, takes an entry specifier and an attribute
      specifier.

   Example:

           C: a FETCH 1 (ANNOTATION (/comment value))
           S: * 1 FETCH (ANNOTATION (/comment
                                       (value.priv "My comment"
                                        value.shared "Group note")))
           S: a OK Fetch complete

      In the above example, the content of the "value" attribute for the
      "/comment" entry is requested by the client and returned by the
      server.  Since neither ".shared" nor ".priv" was specified, both
      are returned.

   "*" and "%" wild card characters can be used in entry specifiers to
   match one or more characters at that position, with the exception
   that "%" does not match the "/" hierarchy delimiter.  Thus, an entry
   specifier of "/%" matches entries such as "/comment" and
   "/altsubject", but not "/1/comment".

   Example:

           C: a UID FETCH 1123 (UID ANNOTATION
                                (/* (value.priv size.priv)))
           S: * 12 FETCH (UID 1123 ANNOTATION
                  (/comment (value.priv "My comment"
                                       size.priv "10")
                   /altsubject (value.priv "Rhinoceroses!"
                                       size.priv "13")
                   /vendor/foobar/label.priv
                                       (value.priv "label43"
                                        size.priv "7")
                   /vendor/foobar/personality
                                       (value.priv "Tallulah Bankhead"
                                        size.priv "17")))
           S: a OK Fetch complete

      In the above example, the contents of the private "value" and
      "size" attributes for any entries in the "/" hierarchy are
      requested by the client and returned by the server.

   Example:

           C: a FETCH 1 (ANNOTATION (/% value.shared))
           S: * 1 FETCH (ANNOTATION
              (/comment (value.shared "Patch Mangler")
               /altsubject (value.shared "Patches?  We don't
               need no steenkin patches!")))
           S: a OK Fetch complete

      In the above example, the contents of the shared "value"
      attributes for entries at the top level only of the "/" hierarchy
      are requested by the client and returned by the server.

   Entry and attribute specifiers can be lists of atomic specifiers, so
   that multiple items of each type may be returned in a single FETCH
   command.

   Example:

           C: a FETCH 1 (ANNOTATION
                ((/comment /altsubject) value.priv))
           S: * 1 FETCH (ANNOTATION
                (/comment (value.priv "What a chowder-head")
                 /altsubject (value.priv "How to crush beer cans")))
           S: a OK Fetch complete

      In the above example, the contents of the private "value"
      attributes for the two entries "/comment" and "/altsubject" are
      requested by the client and returned by the server.

4.4.  ANNOTATION Message Data Item in FETCH Response

   The ANNOTATION message data item in the FETCH response displays
   information about annotations in a message.

   ANNOTATION parenthesized list

      The response consists of a list of entries, each of which have a
      list of attribute-value pairs.

   Example:

           C: a FETCH 1 (ANNOTATION (/comment value))
           S: * 1 FETCH (ANNOTATION (/comment
                                      (value.priv "My comment"
                                       value.shared NIL)))
           S: a OK Fetch complete

      In the above example, a single entry with a single attribute-value
      pair is returned by the server.  Since the client did not specify
      a ".shared" or ".priv" suffix, both are returned.  Only the
      private attribute has a value (the shared value is "NIL").

   Example:

           C: a FETCH 1 (ANNOTATION
                ((/comment /altsubject) value))
           S: * 1 FETCH (ANNOTATION
                (/comment (value.priv "My comment"
                                     value.shared NIL)
                 /altsubject (value.priv "My subject"
                                     value.shared NIL)))
           S: a OK Fetch complete

      In the above example, two entries, each with a single attribute-
      value pair, are returned by the server.  Since the client did not
      specify a ".shared" or ".priv" suffix, both are returned.  Only
      the private attributes have values; the shared attributes are
      "NIL".

   Example:

           C: a FETCH 1 (ANNOTATION
                           (/comment (value size)))
           S: * 1 FETCH (ANNOTATION
                           (/comment
                               (value.priv "My comment"
                                value.shared NIL
                                size.priv "10"
                                size.shared "0")))
           S: a OK Fetch complete

      In the above example, a single entry with two attribute-value
      pairs is returned by the server.  Since the client did not specify
      a ".shared" or ".priv" suffix, both are returned.  Only the
      private attributes have values; the shared attributes are "NIL".

   Servers SHOULD send ANNOTATION message data items in unsolicited
   FETCH responses if an annotation entry is changed by a third-party,
   and the ANNOTATE select parameter was used.  This allows servers to
   keep clients updated with changes to annotations by other clients.

   Unsolicited ANNOTATION responses MUST NOT include ANNOTATION data
   values -- only the entry name of the ANNOTATION that has changed.
   This restriction avoids sending ANNOTATION data values (which may be
   large) to a client unless the client explicitly asks for the value.

   Example:

           C: a STORE 1 +FLAGS (\Seen)
           S: * 1 FETCH (FLAGS (\Seen))
                         ANNOTATION (/comment))
           S: a OK STORE complete

      In the above example, an unsolicited ANNOTATION response is
      returned during a STORE command.  The unsolicited response
      contains only the entry name of the annotation that changed, and
      not its value.

4.5.  ANNOTATION Message Data Item in STORE

   ANNOTATION <parenthesized entry-attribute-value list>

      Sets the specified list of entries by adding or replacing the
      specified attributes with the values provided.  Clients can use
      "NIL" for values of attributes it wants to remove from entries.

   The ANNOTATION message data item used with the STORE command has an
   implicit ".SILENT" behavior.  This means the server does not generate
   an untagged FETCH in response to the STORE command and assumes that
   the client updates its own cache if the command succeeds.  Though
   note, that if the Conditional STORE extension [RFC4551] is present,
   then an untagged FETCH response with a MODSEQ data item will be
   returned by the server as required by [RFC4551].

   If the server is unable to store an annotation because the size of
   its value is too large, the server MUST return a tagged NO response
   with a "[ANNOTATE TOOBIG]" response code.

   If the server is unable to store a new annotation because the maximum
   number of allowed annotations has already been reached, the server
   MUST return a tagged NO response with a "[ANNOTATE TOOMANY]" response
   code.

   Example:

           C: a STORE 1 ANNOTATION (/comment
                                    (value.priv "My new comment"))
           S: a OK Store complete

      In the above example, the entry "/comment" is created (if not
      already present).  Its private attribute "value" is created if not
      already present, or replaced if it exists.  "value.priv" is set to
      "My new comment".

   Example:

           C: a STORE 1 ANNOTATION (/comment
                                    (value.shared NIL))
           S: a OK Store complete

      In the above example, the shared "value" attribute of the entry
      "/comment" is removed by storing "NIL" into the attribute.

   Multiple entries can be set in a single STORE command by listing
   entry-attribute-value pairs in the list.

   Example:

           C: a STORE 1 ANNOTATION (/comment
                                    (value.priv "Get tix Tuesday")
                                    /altsubject
                                    (value.priv "Wots On"))
           S: a OK Store complete

      In the above example, the entries "/comment" and "/altsubject" are
      created (if not already present) and the private attribute "value"
      is created or replaced for each entry.

   Multiple attributes can be set in a single STORE command by listing
   multiple attribute-value pairs in the entry list.

   Example:

           C: a STORE 1 ANNOTATION (/comment
                                    (value.priv "My new comment"
                                     value.shared "foo's bar"))
           S: a OK Store complete

      In the above example, the entry "/comment" is created (if not
      already present) and the private and shared "value" attributes are
      created if not already present, or replaced if they exist.

4.6.  ANNOTATION Interaction with COPY

   The COPY command can be used to move messages from one mailbox to
   another on the same server.  Servers that support the ANNOTATION
   extension MUST, for each message being copied, copy all ".priv"
   annotation data for the current user only, and all ".shared"
   annotation data along with the message to the new mailbox.  The only
   exceptions to this are if the destination mailbox permissions are
   such that either the ".priv" or ".shared" annotations are not
   allowed, or if the destination mailbox is of a type that does not
   support annotations or does not support storing of annotations (a
   mailbox that returns a "NONE" or "READ-ONLY" response code in its
   ANNOTATIONS response), or if the destination mailbox cannot support
   the size of an annotation because it exceeds the ANNOTATIONS value.
   Servers MUST NOT copy ".priv" annotation data for users other than
   the current user.

4.7.  ANNOTATION Message Data Item in APPEND

   ANNOTATION <parenthesized entry-attribute-value list>

      Sets the specified list of entries and attributes in the resulting
      message.

   The APPEND command can include annotations for the message being
   appended via the addition of a new append data item [RFC4466].  The
   new data item can also be used with the multi-append [RFC3502]
   extension that allows multiple messages to be appended via a single
   APPEND command.

   Example:

           C: a APPEND drafts ANNOTATION (/comment
                (value.priv "Don't send until I say so")) {310}
           S: + Ready for literal data
           C: MIME-Version: 1.0
           ...
           C:
           S: a OK APPEND completed

      In the above example, a comment with a private value is added to a
      new message appended to the mailbox.  The ellipsis represents the
      bulk of the message.

4.8.  ANNOTATION Criterion in SEARCH

   ANNOTATION <entry-name> <attribute-name> <value>

   The ANNOTATION criterion for the SEARCH command allows a client to
   search for a specified string in the value of an annotation entry of
   a message.

   Messages that have annotations with entries matching <entry-name>,
   attributes matching <attribute-name>, and the specified string
   <value> in their values are returned in the SEARCH results.  The "*"
   character can be used in the entry name field to match any content in
   those items.  The "%" character can be used in the entry name field
   to match a single level of hierarchy only.

   Only the "value", "value.priv", and "value.shared" attributes can be
   searched.  Clients MUST NOT specify an attribute other than either
   "value", "value.priv", or "value.shared".  Servers MUST return a BAD
   response if the client tries to search any other attribute.

   Example:

           C: a SEARCH ANNOTATION /comment value "IMAP4"
           S: * SEARCH 2 3 5 7 11 13 17 19 23
           S: a OK Search complete

      In the above example, the message numbers of any messages
      containing the string "IMAP4" in the shared or private "value"
      attribute of the "/comment" entry are returned in the search
      results.

   Example:

           C: a SEARCH ANNOTATION * value.priv "IMAP4"
           S: * SEARCH 1 2 3 5 8 13 21 34
           S: a OK Search complete

      In the above example, the message numbers of any messages
      containing the string "IMAP4" in the private "value" attribute of
      any entry are returned in the search results.

4.9.  ANNOTATION Key in SORT

   ANNOTATION <entry-name> <attribute-name>

   The ANNOTATION criterion for the SORT command [RFC5256] instructs the
   server to return the sequence numbers or Unique Identifiers (UIDs) of
   messages in a mailbox, sorted using the values of the specified
   annotations.  The ANNOTATION criterion is available if the server
   returns both ANNOTATE-EXPERIMENT-1 and SORT as supported capabilities
   in the CAPABILITY command response.

   Messages are sorted using the values of the <attribute-name>
   attributes in the <entry-name> entries.

   Clients MUST provide either the ".priv" or ".shared" suffix to the
   attribute name to ensure that the server knows which specific value
   to sort on.

   Only the "value.priv" and "value.shared" attributes can be used for
   sorting.  Clients MUST NOT specify an attribute other than either
   "value.priv" or "value.shared".  Servers MUST return a BAD response
   if the client tries to sort on any other attribute.

   When either "value.priv" or "value.shared" is being sorted, the
   server MUST use the character set value specified in the SORT command
   to determine the appropriate sort order.

   Example:

           C: a SORT (ANNOTATION /altsubject value.shared) UTF-8 ALL
           S: * SORT 2 3 4 5 1 11 10 6 7 9 8
           S: a OK Sort complete

      In the above example, the message numbers of all messages are
      returned, sorted according to the shared "value" attribute of the
      "/altsubject" entry.

   Note that the ANNOTATION sort key must include a fully specified
   entry -- wild cards are not allowed.

4.10.  New ACL Rights

   As discussed in Section 3.4, this extension adds a new "n" right to
   the list of rights provided by the ACL extensions [RFC2086] and
   [RFC4314].

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.

      ann-size          = "NONE" /
                           (("READ-ONLY" / nz-number)
                            [SP "NOPRIVATE"])
                           ; response codes indicating the level of
                           ; support for annotations in a mailbox

      append-ext        =/ att-annotate
                          ; modifies [RFC3501] extension behaviour

      att-annotate      = "ANNOTATION" SP
                               "(" entry-att *(SP entry-att) ")"

      att-search        = "value" / "value.priv" / "value.shared"
                          ; the only attributes that can be searched

      att-sort          = "value.priv" / "value.shared"
                          ; the only attributes that can be sorted

      att-value         = attrib SP value

      attrib            = astring
                          ; dot-separated attribute name
                          ; MUST NOT contain "*" or "%"

      attribs           = attrib / "(" attrib *(SP attrib) ")"
                          ; one or more attribute specifiers

      capability        =/ "ANNOTATE-EXPERIMENT-1"
                          ; defines the capability for this extension

      entries           = entry-match /
                          "(" entry-match *(SP entry-match) ")"

      entry             = astring
                          ; slash-separated path to entry
                          ; MUST NOT contain "*" or "%"

      entry-att         = entry SP "(" att-value *(SP att-value) ")"

      entry-match       = list-mailbox
                          ; slash-separated path to entry
                          ; MAY contain "*" or "%" for use as wild cards

      fetch-att         =/ "ANNOTATION" SP "(" entries SP attribs ")"
                          ; modifies original IMAP fetch-att

      msg-att-dynamic   =/ "ANNOTATION" SP
                             ( "(" entry-att *(SP entry-att) ")" /
                               "(" entry *(SP entry) ")" )
                          ; extends FETCH response with annotation data

      resp-text-code    =/ "ANNOTATE" SP "TOOBIG" /
                           "ANNOTATE" SP "TOOMANY" /
                           "ANNOTATIONS" SP ann-size
                          ; new response codes

      search-key        =/ "ANNOTATION" SP entry-match SP att-search
                           SP value
                          ; modifies original IMAP search-key

      select-param      =/ "ANNOTATE"
                          ; defines the select parameter used with
                          ; ANNOTATE extension

      sort-key          =/ "ANNOTATION" SP entry SP att-sort
                          ; modifies original sort-key

      store-att-flags   =/ att-annotate
                          ; modifies original IMAP STORE command

      value             = nstring / literal8

6.  IANA Considerations

   Entry names MUST be specified in a standards track or IESG approved
   experimental RFC, or fall under the vendor namespace.  Vendor names
   MUST be registered.

   Attribute names MUST be specified in a standards track or IESG
   approved experimental RFC.

   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 Annotate Registration

   Please register the following IMAP Annotate item:

   [] Entry        [] Attribute

   Name: ______________________________

   Description: _______________________

   ____________________________________

   ____________________________________

   Content-Type:_______________________

   Contact person: ____________________

           email:  ____________________

6.2.  Entry Registrations

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

6.2.1.  /comment

   To: iana@iana.org
   Subject: IMAP Annotate Registration

   Please register the following IMAP Annotate item:

   [X] Entry        [] Attribute

   Name: /comment

   Description: Defined in IMAP ANNOTATE extension document.

   Content-Type: text/plain; charset=utf-8

   Contact person: Cyrus Daboo

           email:  cyrus@daboo.name

6.2.2.  /flags

   To: iana@iana.org
   Subject: IMAP Annotate Registration

   Please register the following IMAP Annotate item:

   [X] Entry        [] Attribute

   Name: /flags

   Description: Reserved entry hierarchy.

   Content-Type: -

   Contact person: Cyrus Daboo

           email:  cyrus@daboo.name

6.2.3.  /altsubject

   To: iana@iana.org
   Subject: IMAP Annotate Registration

   Please register the following IMAP Annotate item:

   [X] Entry        [] Attribute

   Name: /altsubject

   Description: Defined in IMAP ANNOTATE extension document.

   Content-Type: text/plain; charset=utf-8

   Contact person: Cyrus Daboo

           email:  cyrus@daboo.name

6.2.4.  /<section-part>/comment

   To: iana@iana.org
   Subject: IMAP Annotate Registration

   Please register the following IMAP Annotate item:

   [X] Entry        [] Attribute

   Name: /<section-part>/comment

   Description: Defined in IMAP ANNOTATE extension document.

   Content-Type: text/plain; charset=utf-8

   Contact person: Cyrus Daboo

           email:  cyrus@daboo.name

6.2.5.  /<section-part>/flags/seen

   To: iana@iana.org
   Subject: IMAP Annotate Registration

   Please register the following IMAP Annotate item:

   [X] Entry        [] Attribute

   Name: /<section-part>/flags/seen

   Description: Defined in IMAP ANNOTATE extension document.

   Content-Type: text/plain; charset=utf-8

   Contact person: Cyrus Daboo

           email:  cyrus@daboo.name

6.2.6.  /<section-part>/flags/answered

   To: iana@iana.org
   Subject: IMAP Annotate Registration

   Please register the following IMAP Annotate item:

   [X] Entry        [] Attribute

   Name: /<section-part>/flags/answered

   Description: Defined in IMAP ANNOTATE extension document.

   Content-Type: text/plain; charset=utf-8

   Contact person: Cyrus Daboo

           email:  cyrus@daboo.name

6.2.7.  /<section-part>/flags/flagged

   To: iana@iana.org
   Subject: IMAP Annotate Registration

   Please register the following IMAP Annotate item:

   [X] Entry        [] Attribute

   Name: /<section-part>/flags/flagged

   Description: Defined in IMAP ANNOTATE extension document.

   Content-Type: text/plain; charset=utf-8

   Contact person: Cyrus Daboo

           email:  cyrus@daboo.name

6.2.8.  /<section-part>/flags/forwarded

   To: iana@iana.org
   Subject: IMAP Annotate Registration

   Please register the following IMAP Annotate item:

   [X] Entry        [] Attribute

   Name: /<section-part>/flags/forwarded

   Description: Defined in IMAP ANNOTATE extension document.

   Content-Type: text/plain; charset=utf-8

   Contact person: Cyrus Daboo

           email:  cyrus@daboo.name

6.3.  Attribute Registrations

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

6.3.1.  value

   To: iana@iana.org
   Subject: IMAP Annotate Registration

   Please register the following IMAP Annotate item:

   [] Entry        [X] Attribute

   Name: value

   Description: Defined in IMAP ANNOTATE extension document.

   Contact person: Cyrus Daboo

           email:  cyrus@daboo.name

6.3.2.  size

   To: iana@iana.org
   Subject: IMAP Annotate Registration

   Please register the following IMAP Annotate item:

   [] Entry        [X] Attribute

   Name: size

   Description: Defined in IMAP ANNOTATE extension document.

   Contact person: Cyrus Daboo

           email:  cyrus@daboo.name

6.4.  Capability Registration

   This document registers "ANNOTATE-EXPERIMENT-1" as an IMAPEXT
   capability.

7.  Internationalization Considerations

   Annotations may contain values that include text strings, and both
   searching and sorting are possible with annotations.  Servers MUST
   follow standard IMAP text normalization, character set conversion,
   and collation rules when such operations are carried out, as would be
   done for other textual fields being searched or sorted on.

8.  Security Considerations

   Annotations whose values are intended to remain private MUST be
   stored in ".priv" values instead of ".shared" values, which may be
   accessible to other users.

   Excluding the above issues, the ANNOTATE extension does not raise any
   security considerations that are not present in the base IMAP
   protocol; these issues are discussed in [RFC3501].

9.  References

9.1.  Normative References

   [RFC2086]  Myers, J., "IMAP4 ACL extension", RFC 2086, January 1997.

   [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.

   [RFC3502]  Crispin, M., "Internet Message Access Protocol (IMAP) -
              MULTIAPPEND Extension", RFC 3502, March 2003.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 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.

   [RFC5234]  Crocker, D., Ed., and P. Overell, "Augmented BNF for
              Syntax Specifications: ABNF", STD 68, RFC 5234, January
              2008.

   [RFC5256]  Crispin, M. and K. Murchison, "Internet Message Access
              Protocol - SORT and THREAD Extensions", RFC 5256, June
              2008.

9.2.  Informative References

   [RFC4551]  Melnikov, A. and S. Hole, "IMAP Extension for Conditional
              STORE Operation or Quick Flag Changes Resynchronization",
              RFC 4551, June 2006.

10.  Acknowledgments

   Many thanks to Chris Newman for his detailed comments on the first
   draft of this document, and to the participants at the ACAP working
   dinner in Pittsburgh.  The participants of the IMAPext working group
   made significant contributions to this work.

Authors' Addresses

   Cyrus Daboo
   Apple Inc.
   1 Infinite Loop
   Cupertino, CA  95014
   USA

   EMail: cyrus@daboo.name
   URI:   http://www.apple.com/

   Randall Gellens
   QUALCOMM Incorporated
   5775 Morehouse Dr.
   San Diego, CA  92121-2779
   USA

   EMail: randy@qualcomm.com

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