[TechTalk] Enabling Postfix in OS X: "From Mac OS X Hints, for people who might enable and run the Postfix
MTA included in OS X Panther:

1. Edit the MAILSERVER=-NO- line in /etc/hostconfig. Change it to
read MAILSERVER=-YES-. Save and exit the file.
2. Open up /etc/postfix/main.cf, and edit these lines to reflect
your setup. These are examples from my setup; yours might be different.
? LINE 67: myhostname = hostname.domain.org
? LINE 75: mydomain = domain.org
? LINE 91: myorigin = $mydomain
? LINE 105: inet_interfaces = all
? LINE 152: mydestination = $myhostname, localhost.$mydomain
? LINE 239: mynetworks_style = subnet
? LINE 253: mynetworks = 192.168.0.0/23, 127.0.0.0/8"