[K12OSN] OT...but I need help with postfix

[Doug Gough]

I can't find any answer to this question anywhere else, so I'm hoping
someone here has some ideas. I run Mandrake 10 as a general purpose
server at my school. I've installed Postfix, and it won't receive mail
from outside. When I run Nmap, it tells me that there is no Port 25.
Port 25 is listed in /etc/services so what's going on? Port 25 is opened
on the firewall as well, but it's just not there on the system. 

Thanks,

Doug Gough