To set the bind address for postfix, do the following.
sudo vi /etc/postfix/main.cf
Locate the section that has the following
inet_interfaces = all
#inet_interfaces = $myhostname
#inet_interfaces = $myhostname, localhost
Add a “#” to all current lines, then add a new line which contains localhost and the ip of your server that you wish people to be able to connect to, separated by a comma. for example
#inet_interfaces = all
#inet_interfaces = $myhostname
#inet_interfaces = $myhostname, localhost
inet_interfaces = localhost, 192.168.2.1
Then restart postfix
sudo service postfix restart
Then check netstat to ensure its now listening on that port.
[root@myserver ~]# netstat -a
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 192.168.2.1:smtp *:* LISTEN
tcp 0 0 localhost:smtp *:* LISTEN
You should now be able to connect to your server on port 25 on the ip address you added to the config file.
Enjoy