Originally Posted by monkfish
Nice update and responsive ISP by the sounds of it!
I seem to recall that its only a warning by postfix that reverse name doesn't match banner name - this should not on its own stop mail being delivered.
Its possible, although I'm certain on this, that could be a dns related issue. Check your /etc/resolv.conf see what nameservers you are using?
If you don't need IPv6, disable it in /etc/postfix/main.cf:
inet_protocols = ipv4