[CentOS] Need help to track an ip port problem

Hi, My centos 4.4 fully updated is going to be used as a mail server. However I did something or i didn't do something and I need some assistance. You see, If I run sendmail in port 25, i can telnet localhost 25 fine. but if I telnet the machine from another machine, the port is refuse. So i tested by running other programs (one at a time) listening to port 25, I cant connect.

So It seems that something is blocking specifically port 25 to receive incoming connections.

Can I have some assistance as to where to look for a configuration mistake? Basically something has my port 25 blocked on the same machine. BTW iptables is not running.

Cheers,