Is there a generally accepted technique to advise (or force) a client to requery the folder list? We currently send an [ALERT], but that's less than optimal.
Unfortunately, no.
Would it make sense to send a bunch of unilateral, untagged LIST responses [ * LIST () "/" foo/bar ], even when the client did not ask?
There has been talk, over the years, of an extension that would use that mechanism to do what you want. Indeed, that sort of thing is exactly why there is a concept of "unsolicited data" in IMAP.
However, this hasn't happened yet. A server can certainly send it, and a client must accept it, but there is no formal definition of the meaning.
Would any known client actually use that information?
Unfortunately, I doubt it.
I fear that some clients might crash. The sad truth is that there is a lot of software out there which does not pay close attention to specifications.
-- Mark --
http://staff.washington.edu/mrc Science does not emerge from voting, party politics, or public debate. Si vis pacem, para bellum.
