IMAP Extensions Working Group                                   B. Leiba
Internet-Draft                           IBM T.J. Watson Research Center
Updates: 2193 (if approved)                                  A. Melnikov
Obsoletes: 3348 (if approved)                              Isode Limited
Expires: September 5, 2006                                 March 4, 2006


                     IMAP4 LIST Command Extensions
                 draft-ietf-imapext-list-extensions-16

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   IMAP4 has two commands for listing mailboxes: LIST and LSUB.  As we
   have added extensions, such as Mailbox Referrals, that have required
   specialized lists we have had to expand the number of list commands,
   since each extension must add its function to both LIST and LSUB, and
   these commands are not, as they are defined, extensible.  If we've
   needed the extensions to work together, we've had to add a set of
   commands to mix the different options, the set increasing in size



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   with each new extension.  This document describes an extension to the
   base LIST command that will allow these additions to be done with
   mutually compatible options to the LIST command, avoiding the
   exponential increase in specialized list commands.

Note

   A revised version of this draft document will be submitted to the RFC
   editor as a Proposed Standard for the Internet Community.  Discussion
   and suggestions for improvement are requested, and should be sent to
   ietf-imapext@imc.org.

   This document obsoletes RFC 3348 and updates RFC 2193.

Table of Contents

   1.  Conventions used in this document  . . . . . . . . . . . . . .  3

   2.  Introduction and overview  . . . . . . . . . . . . . . . . . .  4

   3.  Extended LIST Command  . . . . . . . . . . . . . . . . . . . .  6
   3.1 General principles for returning LIST responses  . . . . . . . 10
   3.2 Additional requirements on LIST-EXTENDED clients . . . . . . . 11
   3.3 CHILDINFO extended data item . . . . . . . . . . . . . . . . . 11

   4.  The CHILDREN return Option . . . . . . . . . . . . . . . . . . 14

   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

   6.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . . 23

   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 27

   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 28
   8.1 Guidelines for IANA  . . . . . . . . . . . . . . . . . . . . . 28
   8.2 Registration procedure and Change control  . . . . . . . . . . 28
   8.3 Registration template for LIST-EXTENDED options  . . . . . . . 29
   8.4 Initial LIST-EXTENDED option registrations . . . . . . . . . . 30
   8.5 Registration template for LIST-EXTENDED extended data item . . 32
   8.6 Initial LIST-EXTENDED extended data item registrations . . . . 33

   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 34

   10. Normative References . . . . . . . . . . . . . . . . . . . . . 34

       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 34

       Intellectual Property and Copyright Statements . . . . . . . . 36



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1.  Conventions used in this document

   In examples, "C:" indicates lines sent by a client that is connected
   to a server.  "S:" indicates lines sent by the server to the client.

   The words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" are
   used in this document as specified in RFC 2119 [Kwds].

   The term "canonical LIST pattern" refers to the canonical pattern
   constructed internally by the server from the reference and mailbox
   name arguments (Section 6.3.8 of [IMAP4]).  The [IMAP4] LIST command
   returns only mailboxes that match the canonical LIST pattern.

   Other terms are introduced where they are referenced for the first
   time.




































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2.  Introduction and overview

   The LIST command is extended by amending the syntax to allow options
   and multiple patterns to be specified.  The list of options replaces
   the several commands that are currently used to mix and match the
   information requested.  The new syntax is backward- compatible, with
   no ambiguity: the new syntax is being used if one of the following
   conditions is true:

   1.  if the first word after the command name begins with a
       parenthesis ("LIST selection options");

   2.  if the second word after the command name begins with a
       parenthesis ("multiple mailbox patterns");

   3.  if the LIST command has more than 2 parameters ("LIST return
       options");

   Otherwise the original syntax is used.

   By adding options to the LIST command, we are announcing the intent
   to phase out and eventually to deprecate the RLIST and RLSUB commands
   described in [MBRef].  We are also defining the mechanism to request
   extended mailbox information, such as is described in the "Child
   Mailbox Extension" [CMbox].  The base LSUB command is not deprecated
   by this extension; rather, this extension adds a way to obtain
   subscription information with more options, with those server
   implementations that support it.  Clients that simply need a list of
   subscribed mailboxes, as provided by the LSUB command, SHOULD
   continue to use that command.

   This document defines an IMAP4 extension that is identified by the
   capability string "LIST-EXTENDED".  The LIST-EXTENDED extension makes
   the following changes to the IMAP4 protocol, which are described in
   more detail in Section 3 and Section 4:

   a.  defines new syntax for LIST command options.

   b.  extends LIST to allow for multiple mailbox patterns.

   c.  adds LIST command selection options: SUBSCRIBED, REMOTE and
       RECURSIVEMATCH.

   d.  adds LIST command return options: SUBSCRIBED and CHILDREN.

   e.  adds new mailbox attributes: "\NonExistent", "\Subscribed",
       "\Remote", "\HasChildren" and "\HasNoChildren".




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   f.  adds CHILDINFO extended data item.


















































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3.  Extended LIST Command

   This extension updates the syntax of the LIST command to allow for
   multiple mailbox patterns to be specified, if they are enclosed in
   parentheses.  A mailbox name matches a list of mailbox patterns if it
   matches at least one mailbox pattern.  If a mailbox name matches
   multiple mailbox patterns from the list, the server SHOULD return
   only a single LIST response.

   Note that the non-extended LIST command is required to treat an empty
   ("" string) mailbox name argument as a special request to return the
   hierarchy delimiter and the root name of the name given in the
   reference parameter (as per [IMAP4]).  However ANY extended LIST
   command (extended in any of 3 ways specified in Section 2, or any
   combination of thereof) MUST NOT treat the empty mailbox name as such
   special request and any regular processing described in this document
   applies.  In particular, if an extended LIST command has multiple
   mailbox names and one (or more) of them is the empty string, the
   empty string MUST be ignored for the purpose of matching.

   Some servers might restrict which patterns are allowed in a LIST
   command.  If a server doesn't accept a particular pattern, it MUST
   silently ignore it.

   The LIST command syntax is also extended in two additional ways: by
   adding a parenthesized list of command options between the command
   name and the reference name (LIST selection options) and an optional
   list of options at the end that control what kind of information
   should be returned (LIST return options).  See the formal syntax in
   Section 6 for specific details.

   A LIST selection option tells the server which mailbox names should
   be selected by the LIST operation.  The server should return
   information about all mailbox names that match any of the "canonical
   LIST pattern" (as described above) and satisfy additional selection
   criteria (if any) specified by the LIST selection options.  Let's
   call any such mailbox name a "matched mailbox name".  When multiple
   selection options are specified, the server MUST return information
   about mailbox names that satisfy every selection option, unless a
   description of a particular specified option prescribes special
   rules.  An example of an option prescribing special rules is the
   RECURSIVEMATCH selection option described later in this section.  We
   will use the term "selection criteria" when referring collectively to
   all selection options specified in a LIST command.

   A LIST return option controls which information is returned for each
   matched mailbox name.  Note that return options MUST NOT cause the
   server to report information about additional mailbox names.  If the



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   client has not specified any return option, only information about
   attributes should be returned by the server.  (Of course the server
   is allowed to include any other information at will.)

   Both selection and return command options will be defined in this
   document and in approved extension documents; each option will be
   enabled by a capability string (one capability may enable multiple
   options), and a client MUST NOT send an option for which the server
   has not advertised support.  A server MUST respond to options it does
   not recognize with a BAD response.  The client SHOULD NOT specify any
   option more than once, however if the client does this, the server
   MUST act as if it received the option only once.  The order in which
   options are specified by the client is not significant.

   In general, each selection option except for RECURSIVEMATCH will have
   a corresponding return option.  The REMOTE selection option is an
   anomaly in this regard, and does not have a corresponding return
   option.  That is because it expands, rather than restricts, the set
   of mailboxes that are returned.  Future extensions to this
   specification should keep parallelism in mind, and define a pair of
   corresponding options.

   This extension is identified by the capability string "LIST-
   EXTENDED", and support for it is a prerequisite for any future
   extensions that require specialized forms of the LIST command.  Such
   extensions MUST refer to this document and MUST add their function
   through command options as described herein.  Note that extensions
   that don't require support for an extended LIST command, but use
   extended LIST responses (see below), don't need to advertise the
   "LIST-EXTENDED" capability string.

   This extension also defines extensions to the LIST response, allowing
   a series of extended fields at the end, a parenthesized list of
   tagged data (also referred to as "extended data item").  The first
   element of an extended field is a tag, which identifies type of the
   data.  Tags MUST be registered with IANA, as described in Section 8.5
   of this document.  An example of such extended set might be

   tablecloth (("edge" "lacy") ("color" "red"))) (X-Sample "text"))

   or...

   tablecloth ("edge" "lacy")) (X-Sample "text" "more text"))

   See the formal syntax, in Section 6, for the full syntactic details.
   The server MUST NOT return any extended data item, unless the client
   has expressed its ability to support extended LIST responses, for
   example by using an extended LIST command.  The server MAY return



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   data in the extended fields that was not directly solicited by the
   client in the corresponding LIST command.  For example, the client
   can enable extra extended fields by using another IMAP extension that
   make use of the extended LIST responses.  The client MUST ignore all
   extended fields it doesn't recognize.

   The LIST-EXTENDED capability also defines several new mailbox
   attributes.

   The "\NonExistent" attribute indicates that a mailbox name does not
   refer to an existing mailbox.  Note that this attribute is not
   meaningful by itself, as mailbox names that match the canonical LIST
   pattern but don't exist must not be returned unless one of the two
   conditions listed below is also satisfied:

   a.  the mailbox name also satisfies the selection criteria (for
       example, it is subscribed and the "SUBSCRIBED" selection option
       has been specified)


   b.  "RECURSIVEMATCH" has been specified, and the mailbox name has at
       least one descendant mailbox name that does not match the LIST
       pattern and does match the selection criteria.

   In practice this means that the "\NonExistent" attribute is usually
   returned with one or more of "\Subscribed", "\Remote" or the
   CHILDINFO extended data item (see their description below).

   The "\NonExistent" attribute implies "\NoSelect".  The "\NonExistent"
   attribute MUST be supported and MUST be accurately computed.

   The selection options defined in this specification are

   SUBSCRIBED - causes the LIST command to list subscribed names, rather
      than the existing mailboxes.  This will often be a subset of the
      actual mailboxes.  It's also possible for this list to contain the
      names of mailboxes that don't exist.  In any case, the list MUST
      include exactly those mailbox names that match the canonical list
      pattern and are subscribed to.  This option is intended to
      supplement the LSUB command.  Of particular note are the mailbox
      attributes as returned by this option, compared with what is
      returned by LSUB.  With the latter, the attributes returned may
      not reflect the actual attribute status on the mailbox name, and
      the \NoSelect attribute has a special meaning (it indicates that
      this mailbox is not, itself, subscribed, but that it has
      descendant mailboxes that are).  With the SUBSCRIBED selection
      option described here, the attributes are accurate, complete, and
      have no special meanings.  "LSUB" and "LIST (SUBSCRIBED)" are,



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      thus, not the same thing, and some servers must do significant
      extra work to respond to "LIST (SUBSCRIBED)".  Because of this,
      clients SHOULD continue to use "LSUB" unless they specifically
      want the additional information offered by "LIST (SUBSCRIBED)".

      This option defines a new mailbox attribute, "\Subscribed", that
      indicates that a mailbox name is subscribed to.  The "\Subscribed"
      attribute MUST be supported and MUST be accurately computed when
      the SUBSCRIBED selection option is specified.

      Note that the SUBSCRIBED selection option implies the SUBSCRIBED
      return option (see below).


   REMOTE - causes the LIST command to show remote mailboxes as well as
      local ones, as described in [MBRef].  This option is intended to
      replace the RLIST command and, in conjunction with the SUBSCRIBED
      selection option, the RLSUB command.

      This option defines a new mailbox attribute, "\Remote", that
      indicates that a mailbox is a remote mailbox.  The "\Remote"
      attribute MUST be accurately computed when the REMOTE option is
      specified.

      The REMOTE selection option has no interaction with other options.
      Its effect is to tell the server to apply the other options, if
      any, to remote mailboxes, in addition to local ones.  In
      particular, it has no interaction with RECURSIVEMATCH (see below).
      A request for (REMOTE RECURSIVEMATCH) is invalid, because a
      request for (RECURSIVEMATCH) is.  A request for (REMOTE
      RECURSIVEMATCH SUBSCRIBED) is asking for all subscribed mailboxes,
      both local and remote.


   RECURSIVEMATCH - this option forces the server to return information
      about parent mailboxes that don't match other selection options,
      but have some submailboxes that do.  Information about children is
      returned in the CHILDINFO extended data item, as described in
      Section 3.3.

      Note 1: In order for a parent mailbox to be returned, it still has
      to match the canonical LIST pattern.

      Note 2: When returning the CHILDINFO extended data item, it
      doesn't matter if the submailbox matches the canonical LIST
      pattern or not.  See also example 9 in Section 5.

      The RECURSIVEMATCH option MUST NOT occur as the only selection



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      option (nor only with REMOTE), as it only makes sense when other
      selection options are also used.  The server MUST return BAD
      tagged response in such case.

      Note that even if RECURSIVEMATCH option is specified, the client
      MUST still be able to handle a case when a CHILDINFO extended data
      item is returned and there are no submailboxes that meet the
      selection criteria of the given LIST command, as they can be
      deleted/renamed after the LIST response was sent, but before the
      client had a chance to access them.

   The return options defined in this specification are

   SUBSCRIBED - causes the LIST command to return subscription state for
      all matching mailbox names.  The "\Subscribed" attribute MUST be
      supported and MUST be accurately computed when the SUBSCRIBED
      return option is specified.  Further, all mailbox flags MUST be
      accurately computed (this differs from the behaviour of the LSUB
      command).


   CHILDREN - Requests mailbox child information as originally proposed
      in [CMbox].  See Section 4, below, for details.  This option MUST
      be supported by all servers.


3.1  General principles for returning LIST responses

   This section outlines several principles that can be used by server
   implementations of this document to decide if a LIST response should
   be returned, as well as how many responses and what kind of
   information they may contain.

   1.  Exactly one LIST response should be returned for each mailbox
       name which matches the canonical LIST pattern.  Server
       implementors must not assume that clients will be able to
       assemble mailbox attributes and other information returned in
       multiple LIST responses.


   2.  There are only two reasons for including a matching mailbox name
       in the responses to the LIST command (Note that the server is
       allowed to return unsolicited responses at any time.  Such
       responses are not governed by this rule):


       A.  the mailbox name also satisfies the selection criteria;




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       B.  the mailbox name doesn't satisfy the selection criteria, but
           it has at least one descendant mailbox name that satisfies
           the selection criteria and that doesn't match the canonical
           LIST pattern.
           For more information on this case see the CHILDINFO extended
           data item described in Section 3.3.  Note that the CHILDINFO
           extended data item can only be returned when the
           RECURSIVEMATCH selection option is specified.


   3.  Attributes returned in the same LIST response must be treated
       additively.  For example the following response


          S: * LIST (\Subscribed \NonExistent) "/" "Fruit/Peach"


       means that the "Fruit/Peach" mailbox doesn't exist, but it is
       subscribed.


3.2  Additional requirements on LIST-EXTENDED clients

   All clients that support this extension MUST treat an attribute with
   a stronger meaning, as implying any attribute that can be inferred
   from it.  For example, the client must treat presence of the
   \NoInferiors attribute as if the \HasNoChildren attribute was also
   sent by the server.

   The following table summarizes inference rules described in
   Section 3.

               +--------------------+-------------------+
               | returned attribute | implied attribute |
               +--------------------+-------------------+
               |    \NoInferiors    |   \HasNoChildren  |
               |                    |                   |
               |    \NonExistent    |     \NoSelect     |
               +--------------------+-------------------+


3.3  CHILDINFO extended data item

   The CHILDINFO extended data item MUST only be returned when the
   client has specified the RECURSIVEMATCH selection option.

   The CHILDINFO extended data item in a LIST response describes the
   selection criteria that has caused it to be returned and indicates



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   that the mailbox has at least one descendant mailbox that matches the
   selection criteria.

   The LSUB command indicates this condition by using the "\NoSelect"
   attribute, but the LIST (SUBSCRIBED) command MUST NOT do that, since
   "\NoSelect" retains its original meaning here.  Further, the
   CHILDINFO extended data item is more general, in that it can be used
   with any extended set of selection criteria.

   The returned selection criteria allow the client to distinguish a
   solicited response from an unsolicited one, as well as to distinguish
   among solicited responses caused by multiple pipelined LIST commands
   that specify different criteria.

   Servers SHOULD ONLY return a non-matching mailbox name along with
   CHILDINFO if at least one matching child is not also being returned.
   That is, servers SHOULD suppress redundant CHILDINFO responses.

   Examples 8 and 10 in Section 5 demonstrate the difference between
   present CHILDINFO extended data item and the "\HasChildren"
   attribute.

   The following table summarizes interaction between the "\NonExistent"
   attribute and CHILDINFO (the first collumn describes if the parent
   mailbox exists):

   +----------------+----------------+----------------+----------------+
   |     exists     |    meets the   |   has a child  |    returned    |
   |                |    selection   | that meets the |  LIST-EXTENDED |
   |                |    criteria    |    selection   | attributes and |
   |                |                |    criteria    |    CHILDINFO   |
   +----------------+----------------+----------------+----------------+
   |       no       |       no       |       no       |     no LIST    |
   |                |                |                |    response    |
   |                |                |                |    returned    |
   |                |                |                |                |
   |       yes      |       no       |       no       |     no LIST    |
   |                |                |                |    response    |
   |                |                |                |    returned    |
   |                |                |                |                |
   |       no       |       yes      |       no       |  (\NonExistent |
   |                |                |                |     <attr>)    |
   |                |                |                |                |
   |       yes      |       yes      |       no       |    (<attr>)    |
   |                |                |                |                |
   |       no       |       no       |       yes      | (\NonExistent) |
   |                |                |                |   + CHILDINFO  |
   |                |                |                |                |



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   |       yes      |       no       |       yes      | () + CHILDINFO |
   |                |                |                |                |
   |       no       |       yes      |       yes      |  (\NonExistent |
   |                |                |                |    <attr>) +   |
   |                |                |                |    CHILDINFO   |
   |                |                |                |                |
   |       yes      |       yes      |       yes      |   (<attr>) +   |
   |                |                |                |    CHILDINFO   |
   +----------------+----------------+----------------+----------------+

   where <attr> is one or more attributes that correspond to the
   selection criteria, for example for the SUBSCRIBED option the <attr>
   is \Subscribed.






































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4.  The CHILDREN return Option

   The CHILDREN return option implements the Child Mailbox Extension,
   originally proposed by Mike Gahrns and Raymond Cheng, of Microsoft
   Corporation.  Most of the information in this section is taken
   directly from their original specification [CMbox].  The CHILDREN
   return option is simply an indication that the client wants this
   information; a server MAY provide it even if the option is not
   specified.

   Many IMAP4 [IMAP4] clients present to the user a hierarchical view of
   the mailboxes that a user has access to.  Rather than initially
   presenting to the user the entire mailbox hierarchy, it is often
   preferable to show to the user a collapsed outline list of the
   mailbox hierarchy (particularly if there is a large number of
   mailboxes).  The user can then expand the collapsed outline hierarchy
   as needed.  It is common to include within the collapsed hierarchy a
   visual clue (such as a ''+'') to indicate that there are child
   mailboxes under a particular mailbox.  When the visual clue is
   clicked the hierarchy list is expanded to show the child mailboxes.
   The CHILDREN return option provides a mechanism for a client to
   efficiently determine if a particular mailbox has children, without
   issuing a LIST "" * or a LIST "" % for each mailbox name.  The
   CHILDREN return option defines two new attributes that MAY be
   returned within a LIST response: \HasChildren and \HasNoChildren.
   While these attributes MAY be returned in response to any LIST
   command, the CHILDREN return option is provided to indicate that the
   client particularly wants this information.  If the CHILDREN return
   option is present, the server MUST return these attributes even if
   their computation is expensive.

   \HasChildren

        The presence of this attribute indicates that the mailbox has
        child mailboxes.  A server SHOULD NOT set this attribute if
        there are child mailboxes, and the user does not have
        permissions to access any of them.  In this case, \HasNoChildren
        SHOULD be used.  In many cases, however, a server may not be
        able to efficiently compute whether a user has access to any
        child mailbox.  Note that even though the \HasChildren attribute
        for a mailbox must be correct at the time of processing of the
        mailbox, a client must be prepared to deal with a situation when
        a mailbox is marked with the \HasChildren attribute, but no
        child mailbox appears in the response to the LIST command.  This
        might happen, for example, due to children mailboxes beig
        deleted or made inaccessible to the user (using access control)
        by another client before the server is able to list them.




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   \HasNoChildren

        The presence of this attribute indicates that the mailbox has NO
        child mailboxes that are accessible to the currently
        authenticated user.

   [[anchor2: Alexey: I don't like this optionality:]]

   In some instances a server that supports the LIST-EXTENDED extension
   might not be able to determine whether a mailbox has children.  For
   example it may have difficulty determining whether there are child
   mailboxes when LISTing mailboxes while operating in a particular
   namespace.  In these cases, a server MAY exclude both the
   \HasChildren and \HasNoChildren attributes in the LIST response.  As
   such, a client can not make any assumptions about whether a mailbox
   has children based upon the absence of a single attribute.  In
   particular, some servers may not be able to combine the SUBSCRIBED
   selection option and CHILDREN return option.  Such servers MUST
   honour the SUBSCRIBED selection option, and they will simply ignore
   the CHILDREN return option if both are requested.  It is an error for
   the server to return both a \HasChildren and a \HasNoChildren
   attribute for the same mailbox.

   Note: the \HasNoChildren attribute should not be confused with the
   IMAP4 [IMAP4] defined attribute \NoInferiors which indicates that no
   child mailboxes exist now and none can be created in the future.

























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5.  Examples

   1:  The first example shows the complete local hierarchy that will be
       used for the other examples.

      C: A01 LIST "" "*"
      S: * LIST (\Marked \NoInferiors) "/" "inbox"
      S: * LIST () "/" "Fruit"
      S: * LIST () "/" "Fruit/Apple"
      S: * LIST () "/" "Fruit/Banana"
      S: * LIST () "/" "Tofu"
      S: * LIST () "/" "Vegetable"
      S: * LIST () "/" "Vegetable/Broccoli"
      S: * LIST () "/" "Vegetable/Corn"
      S: A01 OK done


   2:  In the next example we'll see the subscribed mailboxes.  This is
       similar to, but not equivalent with, <LSUB "" "*">.  Note that
       the mailbox called "Fruit/Peach" is subscribed to, but does not
       actually exist (perhaps it was deleted while still subscribed).
       The "Fruit" mailbox is not subscribed to, but it has two
       subscribed children.  The "Vegetable" mailbox is subscribed and
       has two children, one of them is subscribed as well.

      C: A02 LIST (SUBSCRIBED) "" "*"
      S: * LIST (\Marked \NoInferiors \Subscribed) "/" "inbox"
      S: * LIST (\Subscribed) "/" "Fruit/Banana"
      S: * LIST (\Subscribed \NonExistent) "/" "Fruit/Peach"
      S: * LIST (\Subscribed) "/" "Vegetable"
      S: * LIST (\Subscribed) "/" "Vegetable/Broccoli"
      S: A02 OK done


   3:  The next example shows the use of the CHILDREN option.  The
       client, without having to list the second level of hierarchy, now
       knows which of the top-level mailboxes have submailboxes
       (children) and which do not.  Note that it's not necessary for
       the server to return the \HasNoChildren attribute for the inbox,
       because the \NoInferiors attribute already implies that, and has
       a stronger meaning.

      C: A03 LIST () "" "%" RETURN (CHILDREN)
      S: * LIST (\Marked \NoInferiors) "/" "inbox"
      S: * LIST (\HasChildren) "/" "Fruit"
      S: * LIST (\HasNoChildren) "/" "Tofu"
      S: * LIST (\HasChildren) "/" "Vegetable"
      S: A03 OK done



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   4:  In this example we see more mailboxes that reside on another
       server to which we may obtain referrals.  This is similar to the
       command <RLIST "" "%">.  Note that in the case of the remote
       mailboxes, the server might or might not be able to include
       CHILDREN information; it includes it if it can, and omits it if
       it can't.

      C: A04 LIST (REMOTE) "" "%" RETURN (CHILDREN)
      S: * LIST (\Marked \NoInferiors) "/" "inbox"
      S: * LIST (\HasChildren) "/" "Fruit"
      S: * LIST (\HasNoChildren) "/" "Tofu"
      S: * LIST (\HasChildren) "/" "Vegetable"
      S: * LIST (\Remote) "/" "Bread"
      S: * LIST (\HasChildren \Remote) "/" "Meat"
      S: A04 OK done


   5:  The following example also requests the server to include
       mailboxes that reside on another server.  The server returns
       information about all mailboxes which are subscribed.  This is
       similar to the command <RLSUB "" "*">.  We also see the use of
       two selection options.

      C: A05 LIST (REMOTE SUBSCRIBED) "" "*"
      S: * LIST (\Marked \NoInferiors \Subscribed) "/" "inbox"
      S: * LIST (\Subscribed) "/" "Fruit/Banana"
      S: * LIST (\Subscribed \NonExistent) "/" "Fruit/Peach"
      S: * LIST (\Subscribed) "/" "Vegetable"
      S: * LIST (\Subscribed) "/" "Vegetable/Broccoli"
      S: * LIST (\Remote \Subscribed) "/" "Bread"
      S: A05 OK done


   6:  The following example requests the server to include mailboxes
       that reside on another server.  The server is asked to return
       subscription information for all returned mailboxes.  This is
       different from the example above.

       Note that the output of this command is not a superset of the
       output in the previous example, as it doesn't include LIST
       response for the non-existent "Fruit/Peach".










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      C: A06 LIST (REMOTE) "" "*" RETURN (SUBSCRIBED)
      S: * LIST (\Marked \NoInferiors \Subscribed) "/" "inbox"
      S: * LIST () "/" "Fruit"
      S: * LIST () "/" "Fruit/Apple"
      S: * LIST (\Subscribed) "/" "Fruit/Banana"
      S: * LIST () "/" "Tofu"
      S: * LIST (\Subscribed) "/" "Vegetable"
      S: * LIST (\Subscribed) "/" "Vegetable/Broccoli"
      S: * LIST () "/" "Vegetable/Corn"
      S: * LIST (\Remote \Subscribed) "/" "Bread"
      S: * LIST (\Remote) "/" "Meat"
      S: A06 OK done


   7:  In the following example the client has specified multiple
       mailbox patterns.  Note that this example does not use the
       mailbox hierarchy used in the previous examples.

      C: BBB LIST "" ("INBOX" "Drafts" "Sent/%")
      S: * LIST () "/" "INBOX"
      S: * LIST (\NoInferiors) "/" "Drafts"
      S: * LIST () "/" "Sent/March2004"
      S: * LIST (\Marked) "/" "Sent/December2003"
      S: * LIST () "/" "Sent/August2004"
      S: BBB OK done


   8:  The following example demonstrates the difference between the
       \HasChildren attribute and the CHILDINFO extended data item.

       Let's assume there is the following hierarchy:

      C: C01 LIST "" "*"
      S: * LIST (\Marked \NoInferiors) "/" "inbox"
      S: * LIST () "/" "Foo"
      S: * LIST () "/" "Foo/Bar"
      S: * LIST () "/" "Foo/Baz"
      S: * LIST () "/" "Moo"
      S: C01 OK done

       If the client asks RETURN (CHILDREN) it will get this:

      C: CA3 LIST "" "%" RETURN (CHILDREN)
      S: * LIST (\Marked \NoInferiors) "/" "inbox"
      S: * LIST (\HasChildren) "/" "Foo"
      S: * LIST (\HasNoChildren) "/" "Moo"
      S: CA3 OK done




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       A) Let's also assume that the mailbox "Foo/Baz" is the only
       subscribed mailbox.  Then we get this result:

      C: C02 LIST (SUBSCRIBED) "" "*"
      S: * LIST (\Subscribed) "/" "Foo/Baz"
      S: C02 OK done

       Now, if the client issues <LIST (SUBSCRIBED) "" "%">, the server
       will return no mailboxes (as the mailboxes "Moo", "Foo" and
       "Inbox" are NOT subscribed).  However, if the client issues this:

      C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%"
      S: * LIST () "/" "Foo" ("CHILDINFO" ("SUBSCRIBED"))
      S: C04 OK done

       i.e. the mailbox "Foo" is not subscribed, but it has a child that
       is.

       A1) If the mailbox "Foo" had also been subscribed, the last
       command would return this:

      C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%"
      S: * LIST (\Subscribed) "/" "Foo" ("CHILDINFO" ("SUBSCRIBED"))
      S: C04 OK done

       or even this:

      C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%"
      S: * LIST (\Subscribed \HasChildren) "/" "Foo" ("CHILDINFO"
         ("SUBSCRIBED"))
      S: C04 OK done

       A2) If we assume instead that the mailbox "Foo" is not part of
       the original hierarchy and is not subscribed, the last command
       will give this result:

      C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%"
      S: * LIST (\NonExistent) "/" "Foo" ("CHILDINFO" ("SUBSCRIBED"))
      S: C04 OK done

       B) Now, let's assume that no mailbox is subscribed.  In this case
       the command <LIST (SUBSCRIBED RECURSIVEMATCH) "" "%"> will return
       no responses, as there are no subscribed children (even though
       "Foo" has children).

       C) And finally, suppose that only the mailboxes "Foo" and "Moo"
       are subscribed.  In that case we see this result:




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      C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%" RETURN (CHILDREN)
      S: * LIST (\HasChildren \Subscribed) "/" "Foo"
      S: * LIST (\HasNoChildren \Subscribed) "/" "Moo"
      S: C04 OK done

       (which means that the mailbox "Foo" has children, but none of
       them is subscribed).


   9:  The following example demonstrates that the CHILDINFO extended
       data item is returned whether children mailboxes match the
       canonical LIST pattern or not.

       Let's assume there is the following hierarchy:

      C: D01 LIST "" "*"
      S: * LIST (\Marked \NoInferiors) "/" "inbox"
      S: * LIST () "/" "foo2"
      S: * LIST () "/" "foo2/bar1"
      S: * LIST () "/" "foo2/bar2"
      S: * LIST () "/" "baz2"
      S: * LIST () "/" "baz2/bar2"
      S: * LIST () "/" "baz2/bar22"
      S: * LIST () "/" "baz2/bar222"
      S: * LIST () "/" "eps2"
      S: * LIST () "/" "eps2/mamba"
      S: * LIST () "/" "qux2/bar2"
      S: D01 OK done

       And that the following mailboxes are subscribed:

      C: D02 LIST (SUBSCRIBED) "" "*"
      S: * LIST (\Subscribed) "/" "foo2/bar1"
      S: * LIST (\Subscribed) "/" "foo2/bar2"
      S: * LIST (\Subscribed) "/" "baz2/bar2"
      S: * LIST (\Subscribed) "/" "baz2/bar22"
      S: * LIST (\Subscribed) "/" "baz2/bar222"
      S: * LIST (\Subscribed) "/" "eps2"
      S: * LIST (\Subscribed) "/" "eps2/mamba"
      S: * LIST (\Subscribed) "/" "qux2/bar2"
      S: D02 OK done

       The client issues the following command first:








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      C: D03 LIST (RECURSIVEMATCH SUBSCRIBED) "" "*2"
      S: * LIST () "/" "foo2" ("CHILDINFO" ("SUBSCRIBED"))
      S: * LIST (\Subscribed) "/" "foo2/bar2"
      S: * LIST () "/" "baz2" ("CHILDINFO" ("SUBSCRIBED"))
      S: * LIST (\Subscribed) "/" "baz2/bar2"
      S: * LIST (\Subscribed) "/" "baz2/bar22"
      S: * LIST (\Subscribed) "/" "baz2/bar222"
      S: * LIST (\Subscribed) "/" "eps2" ("CHILDINFO" ("SUBSCRIBED"))
      S: * LIST (\Subscribed) "/" "qux2/bar2"
      S: D03 OK done

       and the server may also include

      S: * LIST (\NonExistent) "/" "qux2" ("CHILDINFO" ("SUBSCRIBED"))

       The CHILDINFO extended data item is returned for mailboxes
       "foo2", "baz2" and "eps2", because all of them have subscribed
       children, even though for the mailbox "foo2" only one of the two
       subscribed children match the pattern, for the mailbox "baz2" all
       the subscribed children match the pattern and for the mailbox
       "eps2" none of the subscribed children matches the pattern.

       Note that if the client issues

      C: D03 LIST (RECURSIVEMATCH SUBSCRIBED) "" "*"
      S: * LIST () "/" "foo2" ("CHILDINFO" ("SUBSCRIBED"))
      S: * LIST (\Subscribed) "/" "foo2/bar1"
      S: * LIST (\Subscribed) "/" "foo2/bar2"
      S: * LIST () "/" "baz2" ("CHILDINFO" ("SUBSCRIBED"))
      S: * LIST (\Subscribed) "/" "baz2/bar2"
      S: * LIST (\Subscribed) "/" "baz2/bar22"
      S: * LIST (\Subscribed) "/" "baz2/bar222"
      S: * LIST (\Subscribed) "/" "eps2" ("CHILDINFO" ("SUBSCRIBED"))
      S: * LIST (\Subscribed) "/" "eps2/mamba"
      S: * LIST (\Subscribed) "/" "qux2/bar2"
      S: D03 OK done

       the LIST responses for mailboxes "foo2", "baz2" and "eps2" still
       have the CHILDINFO extended data item, even though this
       information is redundant and the client can determine it by
       itself.


   10: The following example shows usage of multiple mailbox patterns.
       It also demonstrates that the presence of the CHILDINFO extended
       data item doesn't necessarily imply \HasChildren.





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      C: a1 LIST "" ("foo" "foo/*")
      S: * LIST () "/" foo
      S: a1 OK done

      C: a2 LIST (SUBSCRIBED) "" "foo/*"
      S: * LIST (\Subscribed \NonExistent) "/" foo/bar
      S: a2 OK done

      C: a3 LIST (SUBSCRIBED RECURSIVEMATCH) "" foo RETURN (CHILDREN)
      S: * LIST (\HasNoChildren) "/" foo ("CHILDINFO" ("SUBSCRIBED"))
      S: a3 OK done








































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6.  Formal Syntax

   The following syntax specification uses the augmented Backus-Naur
   Form (BNF) as described in [ABNF].  Terms not defined here are taken
   from [IMAP4].  In particular, note that the version of "mailbox-list"
   below, which defines the payload of the LIST response, updates the
   version defined in the IMAP specification.  It is pointed to by
   "mailbox-data", which is defined in [IMAP4].

   "vendor-token" is defined in [ACAP].  Note that this normative
   reference to ACAP is an issue in moving this spec forward, since it
   introduces a dependency on ACAP.  The definitions of "vendor-token"
   and of the IANA registry must eventually go somewhere else, in a
   document that can be moved forward on the standards track
   independently of ACAP.

   childinfo-extended-item = "CHILDINFO" SP "("
               list-select-base-opt-quoted
               *(SP list-select-base-opt-quoted) ")"
               ; Extended data item (mbox-list-extended-item) ; returned
               when the RECURSIVEMATCH
               ; selection option is specified.
               ; Note 1: the CHILDINFO tag can be returned
               ;  with and without surrounding quotes, as per
               ;  mbox-list-extended-item-tag production.
               ; Note 2: The selection options are always returned
               quoted,
               ;  unlike their specification in the extended LIST
               ;  command.


   child-mbox-flag = "\HasChildren" / "\HasNoChildren"
               ; attributes for CHILDREN return option, at most one
               ; possible per LIST response


   eitem-standard-tag = atom
               ; a tag for extended list data defined in a Standard
               ; Track or Experimental RFC.


   eitem-vendor-tag = vendor-tag
               ; a vendor specific tag for extended list data








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   list =      "LIST" [SP list-select-opts] SP mailbox SP mbox-or-pat
               [SP list-return-opts]


   list-return-opts = "RETURN" SP
               "(" [return-option *(SP return-option)] ")"
               ; list return options, e.g.  CHILDREN


   list-select-base-opt = "SUBSCRIBED" / option-extension
               ; options that can be used by themselves


   list-select-base-opt-quoted = <"> list-select-base-opt <">


   list-select-independent-opt = "REMOTE" / option-extension
               ; options that do not syntactically interact with
               ; other options


   list-select-mod-opt = "RECURSIVEMATCH" / option-extension
               ; options that require a list-select-base-opt
               ; to also be present


   list-select-opt = list-select-base-opt / list-select-independent-opt
               / list-select-mod-opt
               ; An option registration template is described in
               ; Section 8.3 of this document.


   list-select-opts = "(" [
                 (*(list-select-opt SP) list-select-base-opt
                  *(SP list-select-opt))
               / (list-select-independent-opt
                  *(SP list-select-independent-opt))
               ] ")"
               ; Any number of options may be in any order.
               ; If a list-select-mod-opt appears, then a
               ;    list-select-base-opt must also appear.
               ; This allows these:
               ;   ()
               ;   (REMOTE)
               ;   (SUBSCRIBED)
               ;   (SUBSCRIBED REMOTE)
               ;   (SUBSCRIBED RECURSIVEMATCH)
               ;   (SUBSCRIBED REMOTE RECURSIVEMATCH)



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               ; But does NOT allow these:
               ;   (RECURSIVEMATCH)
               ;   (REMOTE RECURSIVEMATCH)


   mailbox-list = "(" [mbx-list-flags] ")" SP
               (DQUOTE QUOTED-CHAR DQUOTE / nil) SP mailbox
               [SP mbox-list-extended]
               ;   This is the list information pointed to by the ABNF
               item ;   "mailbox-data", which is defined in [IMAP4]


   mbox-list-extended = "(" [mbox-list-extended-item
               *(SP mbox-list-extended-item)] ")"


   mbox-list-extended-item = mbox-list-extended-item-tag SP tagged-ext-
               val


   mbox-list-extended-item-tag = astring
               ; The content MUST conform to either "eitem-vendor-tag"
               ; or "eitem-standard-tag" ABNF productions.
               ; A tag registration template is described in this
               ; document in Section 8.5.


   mbox-list-oflag = child-mbox-flag / "\NonExistent" / "\Subscribed" /
               "\Remote"


   mbox-or-pat = list-mailbox / patterns


   option-extension = (option-standard-tag / option-vendor-tag)
               [SP option-value]


   option-standard-tag = atom
               ; an option defined in a Standards Track or
               ; Experimental RFC


   option-val-comp = astring /
               option-val-comp *(SP option-val-comp) /
               "(" option-val-comp ")"





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   option-value = "(" option-val-comp ")"


   option-vendor-tag = vendor-token "-" atom
               ; a vendor specific option, non-standard


   patterns =  "(" list-mailbox *(SP list-mailbox) ")"


   return-option = "SUBSCRIBED" / "CHILDREN" / option-extension


   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] ")"











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7.  Security Considerations

   This document describes syntactic changes to the specification of the
   IMAP4 commands LIST, LSUB, RLIST, and RLSUB, and the modified LIST
   command has the same security considerations as those commands.  They
   are described in [IMAP4] and [MBRef].

   The Child Mailbox Extension provides a client a more efficient means
   of determining whether a particular mailbox has children.  If a
   mailbox has children, but the currently authenticated user does not
   have access to any of them, the server SHOULD respond with a
   \HasNoChildren attribute.  In many cases, however, a server may not
   be able to efficiently compute whether a user has access to any child
   mailbox.  If such a server responds with a \HasChildren attribute,
   when in fact the currently authenticated user does not have access to
   any child mailboxes, potentially more information is conveyed about
   the mailbox than intended.  In most situations this will not be a
   security concern, because if information regarding whether a mailbox
   has children is considered sensitive, a user would not be granted
   access to that mailbox in the first place.

   The CHILDINFO extended data item has the same security considerations
   as the \HasChildren attribute described above.




























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8.  IANA Considerations

8.1  Guidelines for IANA

   It is requested that IANA creates two new registries for LIST-
   EXTENDED options and LIST-EXTENDED response data.  The templates and
   the initial registrations are detailed below.

8.2  Registration procedure and Change control

   Registration of a LIST-EXTENDED option is done by filling in the
   template in Section 8.3 and sending it via electronic mail to
   iana@iana.org.  Registration of a LIST-EXTENDED extended data item is
   done by filling in the template in Section 8.5 and sending it via
   electronic mail to iana@iana.org.  IANA has the right to reject
   obviously bogus registrations, but will perform no review of claims
   made in the registration form.

   A LIST-EXTENDED option/extended data item name that starts with "V-"
   is reserved for vendor specific options/extended data items.  All
   options, whether they are vendor specific or global, should be
   registered with IANA.  If a LIST-EXTENDED extended data item is
   returned as a result of requesting a particular LIST-EXTENDED option,
   the name of the option SHOULD be used as the name of the LIST-
   EXTENDED extended data item.

   Each vendor specific options/extended data item MUST start with their
   vendor-token ("vendor prefix").  The vendor-token MUST be registered
   with IANA, using the [ACAP] vendor subtree registry.

   Standard LIST-EXTENDED option/extended data item names are case
   insensitive.  If the vendor prefix is omitted from a vendor specific
   LIST-EXTENDED option/extended data item name, the rest is case
   insensitive.  The vendor prefix itself is not case-sensitive, as it
   might contain non-ASCII characters.

   While the registration procedures do not require it, authors of LIST-
   EXTENDED options/extended data items are encouraged to seek community
   review and comment whenever that is feasible.  Authors may seek
   community review by posting a specification of their proposed
   mechanism as an Internet- Draft.  LIST-EXTENDED options/extended data
   items intended for widespread use should be standardized through the
   normal IETF process, when appropriate.

   Comments on registered LIST-EXTENDED options/extended response data
   should first be sent to the "owner" of the mechanism and/or to the
   IMAPEXT WG mailing list.  Submitters of comments may, after a
   reasonable attempt to contact the owner, request IANA to attach their



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   comment to the registration itself.  If IANA approves of this, the
   comment will be made accessible in conjunction with the registration
   LIST-EXTENDED options/ extended response data itself.

   Once a LIST-EXTENDED registration has been published by IANA, the
   author may request a change to its definition.  The change request
   follows the same procedure as the registration request.

   The owner of a LIST-EXTENDED registration may pass responsibility for
   the registered option/extended data item to another person or agency
   by informing IANA; this can be done without discussion or review.

   The IESG may reassign responsibility for a LIST-EXTENDED option/
   extended data item.  The most common case of this will be to enable
   changes to be made to mechanisms where the author of the registration
   has died, moved out of contact or is otherwise unable to make changes
   that are important to the community.

   LIST-EXTENDED registrations may not be deleted; mechanisms which are
   no longer believed appropriate for use can be declared OBSOLETE by a
   change to their "intended use" field; such LIST-EXTENDED options/
   extended data items will be clearly marked in the lists published by
   IANA.

   The IESG is considered to be the owner of all LIST-EXTENDED options/
   extended data items which are on the IETF standards track.

8.3  Registration template for LIST-EXTENDED options

   To: iana@iana.org
   Subject: Registration of LIST-EXTENDED option X

   LIST-EXTENDED option name:

   LIST-EXTENDED option type: (One of SELECTION or RETURN)

   Implied return options(s), if the option type is SELECTION: (zero or
   more)

   LIST-EXTENDED option description:

   Published specification (optional, recommended):

   Security considerations:

   Intended usage:
   (One of COMMON, LIMITED USE or OBSOLETE)




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   Person and email address to contact for further information:

   Owner/Change controller:

   (Any other information that the author deems interesting may be added
   below this line.)

8.4  Initial LIST-EXTENDED option registrations

   It is requested that the LIST-EXTENDED option registry be populated
   with the following entries:

   1.  To: iana@iana.org
       Subject: Registration of LIST-EXTENDED option SUBSCRIBED

       LIST-EXTENDED option name: SUBSCRIBED

       LIST-EXTENDED option type: SELECTION

       Implied return options(s): SUBSCRIBED

       LIST-EXTENDED option description: Causes the LIST command to list
       subscribed mailboxes, rather than the actual mailboxes.

       Published specification : XXXX, Section 3.

       Security considerations: XXXX, Section 7.

       Intended usage: COMMON

       Person and email address to contact for further information:
       Alexey Melnikov <Alexey.Melnikov@isode.com>

       Owner/Change controller: iesg@ietf.org



   2.  To: iana@iana.org
       Subject: Registration of LIST-EXTENDED option REMOTE

       LIST-EXTENDED option name: REMOTE

       LIST-EXTENDED option type: SELECTION

       Implied return options(s): (none)

       LIST-EXTENDED option description: causes the LIST command to
       return remote mailboxes as well as local ones, as described in



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       RFC 2193.

       Published specification : XXXX, Section 3.

       Security considerations: XXXX, Section 7.

       Intended usage: COMMON

       Person and email address to contact for further information:
       Alexey Melnikov <Alexey.Melnikov@isode.com>

       Owner/Change controller: iesg@ietf.org



   3.  To: iana@iana.org
       Subject: Registration of LIST-EXTENDED option SUBSCRIBED

       LIST-EXTENDED option name: SUBSCRIBED

       LIST-EXTENDED option type: RETURN

       LIST-EXTENDED option description: Causes the LIST command to
       return subscription state.

       Published specification : XXXX, Section 3.

       Security considerations: XXXX, Section 7.

       Intended usage: COMMON

       Person and email address to contact for further information:
       Alexey Melnikov <Alexey.Melnikov@isode.com>

       Owner/Change controller: iesg@ietf.org



   4.  To: iana@iana.org
       Subject: Registration of LIST-EXTENDED option RECURSIVEMATCH

       LIST-EXTENDED option name: RECURSIVEMATCH

       LIST-EXTENDED option type: SELECTION

       Implied return options(s): (none)

       LIST-EXTENDED option description: Requests that CHILDINFO



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       extended data item (childinfo-extended-item) is to be returned.

       Published specification : XXXX, Section 3.

       Security considerations: XXXX, Section 7.

       Intended usage: COMMON

       Person and email address to contact for further information:
       Alexey Melnikov <Alexey.Melnikov@isode.com>

       Owner/Change controller: iesg@ietf.org



   5.  To: iana@iana.org
       Subject: Registration of LIST-EXTENDED option CHILDREN

       LIST-EXTENDED option name: CHILDREN

       LIST-EXTENDED option type: RETURN

       LIST-EXTENDED option description: Requests mailbox child
       information.

       Published specification : XXXX, Section 3 and Section 4.

       Security considerations: XXXX, Section 7.

       Intended usage: COMMON

       Person and email address to contact for further information:
       Alexey Melnikov <Alexey.Melnikov@isode.com>

       Owner/Change controller: iesg@ietf.org


8.5  Registration template for LIST-EXTENDED extended data item

   To: iana@iana.org
   Subject: Registration of X LIST-EXTENDED extended data item

   LIST-EXTENDED extended data item tag:

   LIST-EXTENDED extended data item description:

   Which LIST-EXTENDED option(s) (and their types) causes this extended
   data item to be returned (if any):



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   Published specification (optional, recommended):

   Security considerations:

   Intended usage:
   (One of COMMON, LIMITED USE or OBSOLETE)

   Person and email address to contact for further information:

   Owner/Change controller:

   (Any other information that the author deems interesting may be added
   below this line.)

8.6  Initial LIST-EXTENDED extended data item registrations

   It is requested that the LIST-EXTENDED extended data item registry be
   populated with the following entries:

   1.  To: iana@iana.org
       Subject: Registration of CHILDINFO LIST-EXTENDED extended data
       item

       LIST-EXTENDED extended data item tag: CHILDINFO

       LIST-EXTENDED extended data item description: The CHILDINFO
       extended data item describes the selection criteria that has
       caused it to be returned and indicates that the mailbox has one
       or more child mailbox that match the selection criteria.

       Which LIST-EXTENDED option(s) (and their types) causes this
       extended data item to be returned (if any): RECURSIVEMATCH
       selection option

       Published specification : XXXX, Section 3.3.

       Security considerations: XXXX, Section 7.

       Intended usage: COMMON

       Person and email address to contact for further information:
       Alexey Melnikov <Alexey.Melnikov@isode.com>

       Owner/Change controller: iesg@ietf.org







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9.  Acknowledgements

   Mike Gahrns and Raymond Cheng of Microsoft Corporation originally
   devised the Child Mailbox Extension and proposed it in 1997; the
   idea, as well as most of the text in Section 4, is theirs.

   This document is the result of discussions on the IMAP4 and IMAPEXT
   mailing lists and is meant to reflect consensus of those groups.  In
   particular, Mark Crispin, Philip Guenther, Cyrus Daboo, Timo
   Sirainen, Ken Murchison, Rob Siemborski, Steve Hole, Arnt
   Gulbrandsen, Larry Greenfield, Dave Cridland and Pete Maclean were
   active participants in those discussions or made suggestions to this
   document.

10.  Normative References

   [ABNF]   Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
            Specifications: ABNF", RFC 4234, October 2005.

   [ACAP]   Newman, C. and J. Myers, "ACAP -- Application Configuration
            Access Protocol", RFC 2244, November 1997.

   [CMbox]  Gahrns, M. and R. Cheng, "", RFC 3348, July 2002.

   [IMAP4]  Crispin, M., "Internet Message Access Protocol - Version
            4rev1", RFC 3501, March 2003.

   [Kwds]   Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", RFC 2119, March 1997.

   [MBRef]  Gahrns, M., "IMAP4 Mailbox Referrals", RFC 2193,
            September 1997.


Authors' Addresses

   Barry Leiba
   IBM T.J. Watson Research Center
   19 Skyline Drive
   Hawthorne, NY  10532
   US

   Phone: +1 914 784 7941
   Email: leiba@watson.ibm.com







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   Alexey Melnikov
   Isode Limited
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   Email: Alexey.Melnikov@isode.com
   URI:   http://www.melnikov.ca/










































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