/usr/share/postfix/main.cf.dist contains a typo in a commented-out example line:
#inet_protocools = ipv4
The correct parameter name is "inet_protocols". Users who uncomment this
line to restrict Postfix to IPv4 will inherit the typo, which Postfix
then reports as an unused parameter warning on reload/restart:
warning: /etc/postfix/main.cf: unused parameter: inet_protocools=ipv4
The correctly-spelled default line below it (inet_protocols = all) remains
in effect instead, so the intended IPv4-only restriction silently has no
effect.