How do you stop outgoing spam?

Mon Sep 9 09:17:08 UTC 2002

Please try to keep this discussion technical and not diverge to 
opinions.  I am not looking for opinions or religion.  I am trying to find 
automated tools/systems/boxes that will stop spam from going *out* from an 
ISP.  The ISP has no servers and allocates IP address space to downstream 
customers who spam.  Yes, I know all about ACLs to block offending 
IPs.  The ISP is willing to buy any box or system to stop outgoing spams 
and thereby stop constantly playing with ACLs.

The spamming is usually done (but not only) from an Internet cafe where the 
spammer inserts a "spammer CD" and blasts away at open mail relays.  When 
SMTP is blocked for that IP, they switch to HTTP and send the spam via MSN, 
Yahoo, Hotmail, Kukamail, Outblaze, Safe-mail, etc. to name just a 
few.  Blocking port 80 is harder since it requires maintaining an ever 
larger list of free public web based mail systems or just block port 80 
entirely.

Technical solutions welcome.

Thanks,
Hank