Oh, I knew there had to be something else behind the scenes...

I was begining to think that my theory on the world moving away from person-to-person contact was actually in the more advanced stages!
One other thought comes to mind though... If you are blocking, or intend to block the email address, then wont this person figure out that you are blocking the email address and thus realize that you folks are onto him?
I think what you may want is a Honeypot type configuration so that you capture the email, or IP address of the email server, and direct it to a virtual server on your network. You could then strip the e-mail of all the "secret" data, and replace it with bogus data and send the e-mail on it's way. Sounds like a lot of work though...
Sorry I couldn't be of more help, just trying to point out a few things for ya...
LF
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality."--Albert Einstein