SMTP over IPv6 : gmail classifying nearly all IPv6 mail as spam since 20140818

Matija Grabnar matija at
Fri Aug 22 11:46:09 CEST 2014

On 08/22/2014 11:24 AM, Bjoern A. Zeeb wrote:
>  and frankly your MX should have reverse mapping and that name 
> (whatever it is) should have some AAAA or A records if you want to do 
> mail (note the forward -> reverse -> forward does not have to end up 
> on the same name, e.g., could be IN MX -> IN AAAA 
> 2001:db8::42 -> 
I host my email at home, and I got a fixed IPv4 address partly for that 
I got native IPv6 from my ISP a few months ago, but I have been 
absolutely unable to get my ISP to delegate IPv6 reverse DNS zone for my 
address space to my server.

In fact, in one of the locations where the $work hosts it's servers, we 
have native IPv6, with a /64 delegated to our racks, and that provider 
is unwilling/unable to delegate the reverse DNS for that address space, 
too. The best I could get out of them was "generate the reverse DNS file 
for your servers, send by email to so-and-so and he will put it up when 
he has the time".

Neither of those machines are sending anything resembling spamn (knock 

So, much as I would LIKE to have reverse IPv6 DNS on my mail servers, in 
some cases it is just not possible.

> Otherwise you were (are) just a random spambot using one of too many 
> addresses a day to send mail. And a lot of people have been 
> implementing a similar policy on IPv4 for years, though this is (was?) 
> in no RFC at all to my best knowledge. /bz — Bjoern A. Zeeb 

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