My idea would be to try it (NO [PLEASENOOP] first; if the client does NOT catch up after this command (the test is very simple to implement), the server can still disconnect the client (which would help for clients not (yet) supporting it).
In that case, just send your PLEASENOOP as an unsolicited OK at the time of the expunge, without waiting for a command from the client. Maybe call it EXPUNGING.
Mark, what would you think about that?
--Arnt
