I needed to send email messages from a PHP form, and the web server at work uses Postfix. So … I’m getting Postfix set up to relay mail for the first time in a decade or two 🙂 I thought I’d just have to edit /etc/postfix/main.cf and add “relayhost = [something.example.com]”.

Nope. The service fails to start with nothing particularly indicative — just a [FAILED] status from the init script. Attempting to start Postfix outside of the init script is far more informative:

[lisa@564240601ac2 init.d]# /usr/sbin/postfix start
postfix: fatal: parameter inet_interfaces: no local interface found for ::1

Turns out I’ve got to edit /etc/postfix/main.cf and tell it to use IPv4 only:

# Enable IPv4, and IPv6 if supported
inet_protocols = ipv4