Greetings, I'm curious to know if anyone has developed a way to block certain keywords to specific recipients.

I have a handful of users that get very specific spam over and over and over again.  I can't globally block this spam as it would lead to numerous false positives, but in the case of these specific users it is an acceptable amount.

I'm essentially trying to find something that goes through the basic algorithm:  Mail to user X, contains keyword xyz, matches content filter rules - rejected.

Any ideas?