According to the short description of the patent, it covers:
"Systems and methods for automatically determining if the recipient of electronic mail that is unknown at the receiving server has left a 'forwarding address' with a forwarding address server, thereby allowing either the receiving server, the sending server, or the sending user (computer system), or any other party to the communication, to automatically send the electronic mail content to the correct new address. In addition to this automatic 'forwarding', the sending user is notified as to the new electronic mail address so as to allow the sending user to update manually, or automatically, the user's individual database of electronic mail addresses."
MacCentral reports that Mail Registry plans to make the patented software available for free, but it will charge around $20 per year in registration fees.