Block sending to specific email?

We are running Exchange 5.5 on a 2000 server. We have a situation in which I have been asked to block email to and from a specific email address. I used the IMS message filter to block incoming email from this person, but can’t figure out how togo the other way. Is there a way to set it up so that email sent to a certain email address from inside our company will not go through? It would be best if it were invisible (as with the Message Filter), but not completely necessary. We can block the entire domain, if that’s the only way to do it, but would prefer to block only the single user. Thanks!