TODO

  * Change the confirmation request mail so that a manual action is required

  * Look for 'Reply-To: noreply@.*' mails, and don't send confirmation request,
    just drop on the floor

  * Add auto-blacklisting, do that senders with N outstanding confirmation
    requests are added to the blacklist

  * Look for mail containing Subject: Confirm: <confirmation string> and don't
    send confirmation requests if found -- it's probably a mail loop.