* Check the SSL certificate's hostname against the hostname we used
  (RFC 3501, section 11.1)
* Add a Gmail "Mailbox" option similar to the IMAP one (or if that is
  not feasible, a checkbutton "Only check inbox").
* Add a per-mailbox check delay setting (probably GConf only, as that
  feature is seldomly needed)
* See if we can add an Evolution data server mailbox backend
