These are the steps to Force postfix to use only IPv4
1. Edit the main postfix configuration file (main.cf)
1. Edit the main postfix configuration file (main.cf)
vi /etc/postfix/main.cf
2. Change inet_protocols setting from
inet_protocols = all
to
inet_protocols = ipv4
3. Restart the postfix service by using the following command.
service postfix restart
Postfix is now configured to use IPv4 only.