Major Description
The problem is that Outlook on one of the connections it opens to IMAP, tries to do IDLE when no mailbox is selected. The problem is that this brilliant MS product don't want to give up, and retries it sometimes 10 requests and sometimes hundreds of them - maybe more. In thew best case it ends up with extra 200kB of "IDLE <-> NO IDLE failed" communication, but sometimes it ends up with Outlook hanged.
The RFC says IDLE is valid also for authenticated state, however behavior is undefined....