Lars Magne Ingebrigtsen <larsi@gnus.org> writes:

> I've been sceptical to supporting IDLE before, since you can only IDLE
> on one mail box at a time.  But it just occurred to me that if you're
> doing client-side splitting, just idling on the INBOX would suffice.

True, but there's another situation where it is very useful.

I split on the server into about 100 IMAP folders, at delivery time.
INBOX is special, as its mail that (in theory) I want to see promptly,
and the rest I only look at when I'm in a mail-processing mode.

So in this case too, IDLE on just INBOX is not only useful but what I'd
want to configure if I could have IDLE on any subset.

Mail.app (not that I want to hold it up as a paragon of virtue, because
top-posting and sending long lines are both antisocial) also downloads
messages from non-INBOX in the background.  It seems to be a bug that
one can't turn that off, but I wonder if it's just doing it every few
minutes, and IDLEing on INBOX the rest of the time.