If the (original) destination address doesn't have an email account, I think the forwarding just bounces it on to the new destination without doing anything to it. If you have the email account for the original recipient, maybe you could write a "filter" (such as in PHP or Perl) that would read the email and rewrite it and send it on to the new address (you probably wouldn't use the built-in forwarding). In the process, you could add "[Auto Fwd]" to the subject line. In theory, it should work, but it's been a long, long time since I dabbled in this kind of stuff (and would have to relearn it). Be sure to browse around this board, as I would think it's been discussed from time to time.