Routing not working 100% of time

We have a Win 2000 server running as a firewall to the internet. We have two NICs, one for internal network other external.

Trouble is the that the internal network can see and use the internet, but when we fire up Outlook to send and receive email from an external POP server the program cannot find the pop server at all.

I have tried rebooting, turning off “routing and Remote access” but nothing seems to get it to work.

Any ideas?

Gary