Issue :--
send-mail: warning: inet_protocols: IPv6 support is disabled: Address family not supported by protocol
send-mail: warning: inet_protocols: configuring for IPv4 support only
postdrop: warning: inet_protocols: IPv6 support is disabled: Address family not supported by protocol
postdrop: warning: inet_protocols: configuring for IPv4 support only
Solution :--
Check below :- inet_protocols in /etc/postfix/main.cf file
more /etc/postfix/main.cf | grep inet_protocols
inet_protocols = all
To disable the messsage, go to /etc/postfix/main.cf and change from:
inet_protocols = all
TO
inet_protocols = ipv4
# /etc/init.d/postfix restart