Posted by Postfix trying to connect via ipv6 but the network doesn’t support IPv6.
One example of error:
status=deferred (connect to aspmx3.googlemail.com[2607:f8b0:4003:c01::1a]:25: Network is unreachable)
For disable ipv6
vi /etc/postfix/main.cf
change line:
inet_protocols = ipv4
/etc/init.d/postfix restart