IPv6-working freemail status

[Florian Weimer]

* Gert Doering:

>> Some mail filters unfortunately consider MX hosts resolving to IPv6 
>> addresses as invalid and the message is rejected because of 
>> that.  
>
> Can you name some specifics?  I've had an MX with IPv6 record since
> 5 years or so, and have not encountered mail unreachables due to that.

MX entries which point to a name lacking an A record cause relatively
widespread interoperability issues, due to sender domain verification
failures.