Exchange internal email spam

[kevin.rouse () mail va gov (Rouse, Kevin)]

I'm currently dealing with a bit of internal email spam.  Though our system
can handle it, the impact is very large.  I'm looking for and exchange
add-on that would have the ability to screen spam types of emails. The only
utilities we have currently deletes the mail after it is delivered.  Out of
almost 100,000 users, one thread of well written spam has generated several
terabytes of email.  I realize it's a user education problem as well, but
think about it, only 30+ users out of 100,000 used "reply to all" in
addressing the spam threads.  Most of these people are only replying to the
distribution list to ask that their name be removed from that distribution
list.  Then you get the others "replying to all" trying to educate the
others not to "reply to all" as he just did.  Each email weighs in at 1-4
meg due to the size of the distribution list and how many times that
distribution list appears in the email. 99.9 percent of the users are
properly educated, but it only takes a few to really generate some trash.
Just think it's not even a Melissa virus problem, but it's nearly as bad in
the larger email systems.

Any help?  An exchange add-on for screening spam email?

Thanks,
Kevin Rouse
   LAN / WAN Systems Security