Mutt seems to be unable to keep an IMAP connection open for long. I use several versions of mutt on several different computers, with several different IMAP accounts. In all cases, I frequently come back to an instance of mutt to find it saying "Mailbox closed".
My muttrc has `set imap_keepalive=450`. Maybe I should reduce the keepalive time even further? But 450 is already twice as often as the IMAP standard requires.
