> This is how three years ago I solved IPv6 problems for all domains
> that have Google as an MX host.
> smtp_dns_reply_filter = pcre:/etc/postfix/smtp_dns_reply_filter
> # /domain ttl IN AAAA address/ action, all case-insensitive.
> # Note: the domain name ends in ".".
> /^\S+\.google.com\.\s+\S+\s+\S+\s+AAAA\s+/ IGNORE
> This drops all AAAA records from Google MX hosts, effectively forcing
> Postfix to deliver over IPv4.
> I adopted this because their PTR lookups did not distinguish between
> 'try again' and 'does not exist', causing them to reject legitimate