In this post we’ll learn how to fix the problem in Gmail with sending emails via the IPv6 protocol.
Our system has detected
that this message does 550-5.7.1 not meet IPv6 sending guidelines regarding
PTR records and 550-5.7.1 authentication.
There are two solutions, one is to set up reverse DNS for the IPv6 in question, and the second is to make Postfix use only the IPv4 protocol.
Edit the file “/etc/postfix/main.cf”:
... inet_protocols = ipv4
Simply assign the value ipv4 to the inet_protocols directive.
Restart postfix:
systemctl restart postfix
Check the new configuration:
postconf inet_protocols
The output should be inet_protocols = ipv4.