Connecting to external mail server from

I’m having trouble with a private addressing scheme. I have set up a win98 machine with a private address (192.168.0.30). On our server, which still has a static, public IP, I bound a private address to TCP/IP (192.168.0.1). Now, on the win98 machine, it is set to point to the server as a proxy. I can access the internet, but now Outlook cannot connect to the mail server at our ISP. This was not a problem when I had a public IP on the win98 machine. What issues do I need to look at here?