In offline operation mode, after the user forces mail check, after it
succeeds, IMAP should probably log out and disconnect to avoid socket
timeout if the connection disappears later. If this isn't done, as it's
currently implemented, when user reconnects to the network and tries to
poll the remote mailbox, IMAP connection just hangs until it times out.
When the connection may be available for the short periods of time, this
may be a critical factor preventing the user from accessing mails.