btw mail server.
if u wanna use ur mailserver not only for system messages:
consider fighting spam with the greatest ever anti-spam tool.
its called assp (
http://www.assp.sf.net)
its a smtp proxy, written in perl (huhu)
its not the most performant machine on the planet but the most versatile.
and through perl its platform independend, its getting placed between your mailserver and the evil i-net.
it can swallow a whole message for processing and still say "nobody @ home, im sry m8", thats the reason why its a proxy.
through its transparency the spammers will talk to the mailserver herself, it will just jump in for the case that somethings wrong.
ah and again:
if u dont have expirience with smtp:
start over with postfix, read bout smtp auth and control regularly for relay attacks.
dont become a zombie! read bout smtp auth! dont let messages beeing delivered that dont belong to the local domains list!
opening the 25 means participating in a series of crap, established in 1982.