Just a note, to make sure to use BOTH options:

1. Brian's suggestion to HIDE the messages (thanks, Brian, I've been looking
for that for a while)

2. Foor's suggestion to DELETE the messages on exit.

If you just hide them, you'll never know that your email box is actually
growing larger and larger with hidden, but not deleted emails.

Floor, I have Outlook 2003 and can't seem to find that option. Can you tell
me at least where it is in Express? (or anyone else, where in 2003?)

Ok, reading around on this board, I think I'm getting that Outlook 2003 does
not have the option.

Thanks to another post, I have put a macro on a button to purge deleted mail
from all my IMAP Inboxes with the click of one button.

So, my advise here, is NOT to hide the deleted-not-purged messages, because
of the resultant huge mailbox, the performance hit, and of course that you
will fill your box and not be able to receive any more mail, even though you
THINK your box is not full.

..... and to implement the purge macro.

.....and I just noticed, this thread is very old! ooops.
Well, for reference, I guess.