RFC 3348 (rfc3348) - Page 2 of 6

The Internet Message Action Protocol (IMAP4) Child Mailbox Extension

RFC 3348             IMAP4 Child Mailbox Extension             July 2002


   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.

   Several IMAP vendors implemented this proposal, and it is proposed to
   document this behavior and functionality as an Informational RFC.

   There is interest in addressing the general extensibility of the IMAP
   LIST command through an IMAP LIST Extension draft.  Similar
   functionality to the \HasChildren and \HasNoChildren flags could be
   incorporated into this new LIST Extension.  It is proposed that the
   more general LIST Extension draft proceed on the standards track with
   this proposal being relegated to informational status only.

   If the functionality of the \HasChildren and \HasNoChildren flags
   were incorporated into a more general LIST extension, this would have
   the advantage that a client could then have the opportunity to
   request whether or not the server should return this information.
   This would be an advantage over the current draft for servers where
   this information is expensive to compute, since the server would only
   need to compute the information when it knew that the client
   requesting the information was able to consume it.

3. Requirements

   IMAP4 servers that support this extension MUST list the keyword
   CHILDREN in their CAPABILITY response.

   The CHILDREN extension defines two new attributes that MAY be
   returned within a LIST response.

   \HasChildren - The presence of this attribute indicates that the
   mailbox has child mailboxes.

   Servers SHOULD NOT return \HasChildren if child mailboxes exist, but
   none will be displayed to the current user in a LIST response (as
   should be the case where child mailboxes exist, but a client does not
   have permissions to access 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 all child mailboxes, or multiple
   users may be accessing the same account and simultaneously changing
   the mailbox hierarchy.  As such a client MUST be prepared to accept
   the \HasChildren attribute as a hint.  That is, a mailbox MAY be
   flagged with the \HasChildren attribute, but no child mailboxes will
   appear in a subsequent LIST response.




Gahrns, et al.               Informational