Blocking writes in IMAP IDLE
The problem (at least in the second dump) is that we're doing new-message notification to an IMAP connection running the IDLE command, and the write is blocking for some reason. Unfortunately, the lock on the Mailbox is being held by this thread, so everything else backs up waiting for the write to finish and the lock to be released. And the write never finishes.
This will almost certainly go away when we switch to our new IMAP/POP/LMTP framework, as it does network writes from a different thread pool. For now, we'll see what we can do to figure out a temporary workaround.
Thanks very much for the full thread dump!