Here is my environment. I have a Windows 2000 Server(sp2) running Exchange 5.5 (sp4). I have some POP users and some regular corporate users (exchange users). The issue that I am having is that I keep on getting people taking advantage of my Exchange server to send out spam via the open relay. I follow Microsoft's directions on how to shut that down, but my POP users can't send email after that. They can receive, but cannot send. I was wondering if you could help in this issue.