Well, two things...
1. You site must have a valid DNS lookup name. This is a regular URL like
http://www.mysite.com. The server list takes your server name and gets the IP address for it and then compares that to the IP address that sent in the information. If they don't match the info is discarded.
2. You must have your scheduler running. There is an entry in the scheduler that will update your entry in the server list every hour. If the server list doesn't hear from your server for two hours you are removed from the server list. So you need to make sure your cron task is running the scheduler.php every 5 minutes.