offlineIMAP/docs/rfcs/rfc5258.IMAP4_LIST_command_extension.txt

Network Working Group                                           B. Leiba
Request for Comments: 5258               IBM T.J. Watson Research Center
Obsoletes: 3348                                              A. Melnikov
Updates: 2193                                              Isode Limited
Category: Standards Track                                      June 2008


  Internet Message Access Protocol version 4 - LIST Command Extensions

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   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
   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.





















Leiba & Melnikov            Standards Track                     [Page 1]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


Table of Contents

   1.  Introduction and Overview  . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  4
   3.  Extended LIST Command  . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Initial List of Selection Options  . . . . . . . . . . . .  7
     3.2.  Initial List of Return Options . . . . . . . . . . . . . .  8
     3.3.  General Principles for Returning LIST Responses  . . . . .  9
     3.4.  Additional Requirements on LIST-EXTENDED Clients . . . . .  9
     3.5.  CHILDINFO Extended Data Item . . . . . . . . . . . . . . . 10
   4.  The CHILDREN Return Option . . . . . . . . . . . . . . . . . . 11
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   6.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . . 19
   7.  Internationalization Considerations  . . . . . . . . . . . . . 22
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23
     9.1.  Guidelines for IANA  . . . . . . . . . . . . . . . . . . . 23
     9.2.  Registration Procedure and Change Control  . . . . . . . . 23
     9.3.  Registration Template for LIST-EXTENDED Options  . . . . . 25
     9.4.  Initial LIST-EXTENDED Option Registrations . . . . . . . . 25
     9.5.  Registration Template for LIST-EXTENDED Extended Data
           Item . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
     9.6.  Initial LIST-EXTENDED Extended Data Item Registrations . . 28
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 29
     11.2. Informative References . . . . . . . . . . . . . . . . . . 30
























Leiba & Melnikov            Standards Track                     [Page 2]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


1.  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".




Leiba & Melnikov            Standards Track                     [Page 3]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   f.  adds CHILDINFO extended data item.

2.  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 key 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.

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 1, or any
   combination thereof) MUST NOT treat the empty mailbox name as such a
   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






Leiba & Melnikov            Standards Track                     [Page 4]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   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
   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 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



Leiba & Melnikov            Standards Track                     [Page 5]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   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 the type of
   data.  Tags MUST be registered with IANA, as described in Section 9.5
   of this document.  An example of such an 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
   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",
   "\HasChildren", or the CHILDINFO extended data item (see their
   description below).



Leiba & Melnikov            Standards Track                     [Page 6]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


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

3.1.  Initial List of Selection Options

   The selection options defined in this specification are as follows:

   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 second 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 and complete, and have no special meanings.  "LSUB" and
      "LIST (SUBSCRIBED)" are, 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



Leiba & Melnikov            Standards Track                     [Page 7]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


      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 3.5.

      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 whether or not the submailbox matches the canonical
      LIST pattern.  See also example 9 in Section 5.

      The RECURSIVEMATCH option MUST NOT occur as the only selection
      option (or 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 the 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 subsequent LIST command, as
      they can be deleted/renamed after the LIST response was sent, but
      before the client had a chance to access them.

3.2.  Initial List of Return Options

   The return options defined in this specification are as follows:

   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 behavior 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.





Leiba & Melnikov            Standards Track                     [Page 8]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


3.3.  General Principles for Returning LIST Responses

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

   1.  At most one LIST response should be returned for each mailbox
       name that 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, and such
       responses are not governed by this rule):

       A.  The mailbox name also satisfies the selection criteria.

       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 3.5.  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.

3.4.  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 the presence of the
   \NoInferiors attribute as if the \HasNoChildren attribute was also
   sent by the server.






Leiba & Melnikov            Standards Track                     [Page 9]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   The following table summarizes inference rules described in
   Section 3.

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

3.5.  CHILDINFO Extended Data Item

   The CHILDINFO extended data item MUST NOT be returned unless 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
   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.

   Note: Some servers allow for mailboxes to exist without requiring
   their parent to exist.  For example, a mailbox "Customers/ABC" can
   exist while the mailbox "Customers" does not.  As CHILDINFO extended
   data item is not allowed if the RECURSIVEMATCH selection option is
   not specified, such servers SHOULD use the "\NonExistent
   \HasChildren" attribute pair to signal to the client that there is a
   descendant mailbox that matches the selection criteria.  See example
   11 in Section 5.

   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.




Leiba & Melnikov            Standards Track                    [Page 10]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   The following table summarizes interaction between the "\NonExistent"
   attribute and CHILDINFO (the first column indicates whether the
   parent mailbox exists):

   +--------+--------------+--------------------+----------------------+
   | exists |   meets the  |  has a child that  |       returned       |
   |        |   selection  |      meets the     |     LIST-EXTENDED    |
   |        |   criteria   | selection criteria |    attributes and    |
   |        |              |                    |       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      |
   |   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.

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



Leiba & Melnikov            Standards Track                    [Page 11]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   clicked, the hierarchy list is expanded to show the child mailboxes.
   The CHILDREN return option provides a mechanism for a client to
   efficiently determine whether 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 MUST be
   returned within a LIST response: \HasChildren and \HasNoChildren.
   Although 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 permission 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 being deleted or made
        inaccessible to the user (using access control) by another
        client before the server is able to list them.

   \HasNoChildren

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

   It is an error for the server to return both a \HasChildren and a
   \HasNoChildren attribute in the same LIST response.

   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.










Leiba & Melnikov            Standards Track                    [Page 12]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


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 will 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




Leiba & Melnikov            Standards Track                    [Page 13]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   4:   In this example, we see more mailboxes that reside on another
        server.  This is similar to the command <RLIST "" "%">.

      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 that 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".

      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



Leiba & Melnikov            Standards Track                    [Page 14]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   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

   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




Leiba & Melnikov            Standards Track                    [Page 15]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   (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:

      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 or not children mailboxes match
        the canonical LIST pattern.







Leiba & Melnikov            Standards Track                    [Page 16]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


        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:

      C: D03 LIST (RECURSIVEMATCH SUBSCRIBED) "" "*2"
      S: * LIST () "/" "foo2" ("CHILDINFO" ("SUBSCRIBED"))
      S: * LIST (\Subscribed) "/" "foo2/bar2"
      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 (but this would violate a SHOULD NOT
   in Section 3.5, because CHILDINFO is redundant)

      S: * LIST () "/" "baz2" ("CHILDINFO" ("SUBSCRIBED"))
      S: * LIST (\NonExistent) "/" "qux2" ("CHILDINFO" ("SUBSCRIBED"))





Leiba & Melnikov            Standards Track                    [Page 17]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   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 matches 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.

      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

   11:  The following example shows how a server that supports missing
        mailbox hierarchy elements can signal to a client that didn't
        specify the RECURSIVEMATCH selection option that there is a
        child mailbox that matches the selection criteria.





Leiba & Melnikov            Standards Track                    [Page 18]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


      C: a1 LIST (REMOTE) "" *
      S: * LIST () "/" music/rock
      S: * LIST (\Remote) "/" also/jazz
      S: a1 OK done

      C: a2 LIST () "" %
      S: * LIST (\NonExistent \HasChildren) "/" music
      S: a2 OK done

      C: a3 LIST (REMOTE) "" %
      S: * LIST (\NonExistent \HasChildren) "/" music
      S: * LIST (\NonExistent \HasChildren) "/" also
      S: a3 OK done

      C: a3.1 LIST "" (% music/rock)
      S: * LIST () "/" music/rock
      S: a3.1 OK done

   Because "music/rock" is the only mailbox under "music", there's no
   need for the server to also return "music".  However clients must
   handle both cases.

6.  Formal Syntax

   The following syntax specification uses the Augmented Backus-Naur
   Form (ABNF) 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 will be 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.














Leiba & Melnikov            Standards Track                    [Page 19]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   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-token "-" atom
               ; a vendor-specific tag for extended list data

   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 =  DQUOTE list-select-base-opt DQUOTE

   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 9.3 of this document.



Leiba & Melnikov            Standards Track                    [Page 20]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   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)
               ; 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 9.5.

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

   mbx-list-sflag =/  "\NonExistent"

   mbox-or-pat =  list-mailbox / patterns

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





Leiba & Melnikov            Standards Track                    [Page 21]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   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 ")"

   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".
               ; A URL should be represented as
               ; a "quoted" string.

   tagged-ext-simple =  sequence-set / number

   tagged-ext-val =  tagged-ext-simple /
               "(" [tagged-ext-comp] ")"

7.  Internationalization Considerations

   The LIST command selection option types defined in this specification
   involve simple tests of mailbox properties.  However, future
   extensions to LIST-EXTENDED may define selection options that do more
   sophisticated tests.  In the case of a test that requires matching
   text, in the presence of the COMPARATOR [I18N] extension, the active
   comparator must be used to do comparisons.  Such LIST-EXTENDED
   extensions MUST indicate in their specification the interaction with
   the COMPARATOR [I18N] extension.







Leiba & Melnikov            Standards Track                    [Page 22]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


8.  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.

9.  IANA Considerations

9.1.  Guidelines for IANA

   IANA has created two new registries for LIST-EXTENDED options and
   LIST-EXTENDED response data.  The templates and the initial
   registrations are detailed below.

9.2.  Registration Procedure and Change Control

   Registration of a LIST-EXTENDED option is done by filling in the
   template in Section 9.3 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 9.5 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,




Leiba & Melnikov            Standards Track                    [Page 23]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


   the name of the option SHOULD be used as the name of the
   LIST-EXTENDED extended data item.

   Each vendor-specific option/extended data item MUST start with its
   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 option/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
   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, has 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 that 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.



Leiba & Melnikov            Standards Track                    [Page 24]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


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

9.3.  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)

   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.)

9.4.  Initial LIST-EXTENDED Option Registrations

   The LIST-EXTENDED option registry has been 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.




Leiba & Melnikov            Standards Track                    [Page 25]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


       Published specification: RFC 5258, Section 3.

       Security considerations: RFC 5258, Section 8.

       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
       RFC 2193.

       Published specification: RFC 5258, Section 3.

       Security considerations: RFC 5258, Section 8.

       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: RFC 5258, Section 3.

       Security considerations: RFC 5258, Section 8.



Leiba & Melnikov            Standards Track                    [Page 26]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


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

       Published specification: RFC 5258, Section 3.

       Security considerations: RFC 5258, Section 8.

       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: RFC 5258, Section 3 and Section 4.

       Security considerations: RFC 5258, Section 8.

       Intended usage: COMMON

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



Leiba & Melnikov            Standards Track                    [Page 27]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


       Owner/Change controller: iesg@ietf.org

9.5.  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):

   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.)

9.6.  Initial LIST-EXTENDED Extended Data Item Registrations

   The LIST-EXTENDED extended data item registry has been 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 mailboxes 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




Leiba & Melnikov            Standards Track                    [Page 28]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


       Published specification: RFC 5258, Section 3.5.

       Security considerations: RFC 5258, Section 8.

       Intended usage: COMMON

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

       Owner/Change controller: iesg@ietf.org

10.  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.

11.  References

11.1.  Normative References

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

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

   [I18N]   Newman, C., Gulbrandsen, A., and A. Melnikov, "Internet
            Message Access Protocol Internationalization", RFC 5255,
            June 2008.

   [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.




Leiba & Melnikov            Standards Track                    [Page 29]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


11.2.  Informative References

   [CMbox]  Gahrns, M. and R. Cheng, "The Internet Message Action
            Protocol (IMAP4) Child Mailbox Extension", RFC 3348,
            July 2002.

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


   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/
























Leiba & Melnikov            Standards Track                    [Page 30]

RFC 5258             IMAP4 LIST Command Extensions             June 2008


Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.












Leiba & Melnikov            Standards Track                    [Page 31]