Does anyone have recommendations for other products/software to filter our outgoing email, from our customers going to the internet.

For Roll-your-own it's hard to beat a combo of MIMEDefang/SA/Clam (MD is a milter, so sendmail or postfix needed). The MIMEDefang developer also started a company which sells CanIT Pro, an appliance version of the above with additional features/web interface/support Ironport (reassuringly expensive) has worked great here at work. ~JasonG