getting SMTP mail to the AMS

Hi, I have worked with my ISP for some time on getting AMS to receive mail. Originally we had a Eudora Mail Server running on our old Mac File Server (AppleShareIP6.2). When we tried to set up AMS on the XServer the only way we could get it to work is to keep the old mail server in the loop and forward mail from it to AMS. Out going mail works fine. Does any one have insight on what could be blocking me from getting SMTP mail. I want to but the old Eudora Mail Server out to pasture. Thanks. Scott E.