Other Firewalls were considered better at blocking ports, handling traffic, etc. In many large companies, ISA became the internal Firewall, protecting Microsoft servers while the external Firewall was by another vendor. As part of the extensive documentation effort that always set Microsoft apart from other companies, Microsoft now releases detailed information regarding its application layer protection for Exchange.
Get it here:
http://www.microsoft.com/technet/prodtechnol/isa/2004/plan/firewall-exchange2003.mspx
Personally, I am happy to get this document as I'll be implementing my own ISA 2004 Firewall soon, after years of implementing mostly Checkpoint products. My sources at Microsoft tell me that ISA 2006 is now in an advanced beta stage though no details are yet available at this point.
Check out our sister website http://www.isaserver.org for more ISA server information.
