Internet Mail Service -W2K to Exch 5.5

I have a win 2000 box configured to use Internet E-mail and a dial-up connection to get e-mail from an Exchange 5.5 server. When a dial up connection is made I recieve a message that server xxx.xxx.xxx.xxx cannot be found. If I go to DOS I can ping the server no problem. I did notice that the subnet mask is 255.255.255.255. all win98 clients have 255.255.255.0