Allow IPv6 only hosts to properly send emails to IPv4 only hosts
Currently IPv6 only hosts get NAT64'ed to one of our IPv4 addresses. When there is a mail server running on an IPv6 only host that connects to an IPv4 host using the source address 184.108.40.206 .
This again is reverse DNS based mapped to 185-203-114-1.legacy.ipv4.at.ungleich.ch and usually does not fit the EHLO message of the mail server.
We need to find a nice fix for this problem short term so that people can run their mail server in IPv6 only networks