Way to block Incoming/Outgoing spam email
You can configure the rule at /etc/cpanel_exim_system_filter to block for Incoming/outgoing spam email
As tested, it work perfect to stop those email.
Sample Log:
2009-04-18 14:06:42 1Lv3hK-0001Y9-64 Message FROM hploh@rv.iluvbear.com TO test@test,cim is PHISHING – SUBJECT: banking online
Drawback is
-if configure to send the response to the sender, it might cause failed loop and create more work to the mail system, without the response, users might complaint 
-second, some of the user might define the send from as other email account such as, test@yahoo.com. with the new configuration, it reject the outgoing mail from yahoo, hotmail, etc
Anyway, to prevent upcp revert the cpanel_exim_system_filter setting, you could touch a file with a new name and include it at WHM > Exim Configuration Editor> System Filter File
For the old cpanel version (cpanel 10), you shall look for this file:
/etc/antivirus.exim
*http://www.webhostgear.com/338.html