I went through that document but it doesn't show how to to do for a Warm Stand-by system (HA). Also, I have a question with this setup. Assuming my DMZ server has a public IP which Im NAT'ing 1:1 to my active MX public IP. This will be ok for sessions initiated from the DMZ server towards the Internet but for outside sessions trying to reach the public IP Address of my DMZ server, and assuming my MX Public IP is provided by a different ISP from the ISP providing the DMZ server public IP, then sites out on the INterenet will never be able to reach my DMZ Web server.
Juan-Carlos Perez