ports needed to be open for a normal hosting operation
You may find some info in http://www.ehcp.net/helper/yardim/cat.php?cid=6&qid=59
or helper homepage, http://www.ehcp.net/helper/yardim/cats.php
You need to open ports 20,21,22,25,53,80,110,143 on your server and on your modem/firewall/router...
if you have no firewall on your server, you dont need to do anything on your server... But, some users put firewall or extreme security programs so that nobody can reach them... Please avoid this...
You may check your open ports at http://www.ehcp.net/other/portstatus.php