apache: what site is sending email from www-data

[jack <lists@qnorth.net>]

I've had this sort of thing happen a few times, and I'm wondering if 
anyone know's any way to figure it out, or prevent it:

You have say, 50 websites running on your webserver (mostly PHP, some 
cgi). You start to notice your webserver is sending out HUGE amount of 
email (which is spam). Looking at any of the messages in the mail queue, 
you notice all the messages are coming from www-data@host.mydomain.tld, 
so I know they are coming from apache, but what site is it coming from!?!

I've been curious about running PHP under fastcgi w/apache2 with 
FastCGIsuEXEC enabled for each site. From what I understand, doing this 
would make the example I gave before send out mail from 
(UID-SET)@host.mydomain.tld (rather then www-data) which would do 
exactly as I'd want.

What's your experience with this sort of thing? Any suggestions?

Thanks...