How to disable IPv6 for postfix service node?

Symptoms

How to disable IPv6 on a Postfix Service Node?

Resolution

Enforcing Postfix to use IPv4 an be done by specifying inet_protocols parameter in main.cf configuration file:

Open /etc/postfix/main.cf with text editor (for example, vi) on the Postfix service node.
Change inet_protocols value from inet_protocols = all to inet_protocols = ipv4.
Restart Postfix service:
```
# /etc/init.d/postfix restart
```

It defines what protocols Postfix will use, when it makes or accepts network connections, and also controls what DNS lookups Postfix will use, when it makes network connections.