[Imap-protocol] IMAP mutual exclusion

[Bill Shannon]

I occasionally get questions from people who want to have multiple
clients process the messages in a single mailbox.  Usually this
is done to balance load across multiple clients.  Each message in
the mailbox needs to be processed by exactly one client.

Is there a well-defined way for clients to coordinate the processing
of messages in the mailbox using the IMAP protocol?  Is there an
equivalent of "test and set" in the IMAP protocol?  Or is one of the
newer extensions required?