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
