win2k srv with nat used for IP mapping

configuring a MS win2000 based gateway/nat server I have the following issue:
i want port 25 to be forwarded from a public ip on my servers wan adapter to the private ip of my mailserver on the lan.

I can see NAT making the mappings however testing the setup with telnet over port 25 I can’t get the smtp session going.

could anyone direct me to proper reading material on the web on how to properly set this up?

I’ve tried this using the ‘special port’ feature on the NAT servers wan adapter both tcp and udp. Other NAT features work satisfactory on this server.

thanks a million!