Problem installing Postfix

First, check the interfaces that postfix is listening on:

$ netstat  -ltn | grep ":25"
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      
tcp        0      0 <your_ip_here>:25          0.0.0.0:*               LISTEN</your_ip_here> 

If you are only listening on localhost, more than likely your inet_interfaces variable in /etc/postfix/main.cf is the culprit.

inet_interfaces = $myhostname, localhost

Of course, make sure that myhostname is defined correctly somewhere above that.

Bingo - my inet_interfaces variable was exactly what was wrong.

Many thanks,

Michael