RFC 3348 (rfc3348) - Page 2 of 6
The Internet Message Action Protocol (IMAP4) Child Mailbox Extension
Alternative Format: Original Text Document
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