[Cryptography] IPv6 and IPSEC

[Moritz]

> Since forward and reverse DNS will rarely match for IP addresses used by individuals 
> rather than service providers, this change precludes home users of
> IPv6 from sending email to Gmail acccount.

> Note that this new restriction imposed by Gmail only applies to IPv6 addresses, not 
> IPv4 addresses.

For many years now, most mail servers have been rejecting mails sent
from "dynamic IPs". And for IPv6 specifically, long before Gmail, a lot
of ISPs already required forward and reverse DNS to match.

--Mo