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

Bjoern A. Zeeb bzeeb-lists at
Fri Aug 22 11:24:48 CEST 2014

On 22 Aug 2014, at 08:09 , Daniel Austin <daniel at> wrote:

> On 22/08/2014 08:56, Laurent GUERBY wrote:
>> Hi,
>> We've been running SMTP over IPv6 with postfix successfully for over a
>> year and since 20140818 IPv6 MX started to classify most IPv6
>> sourced emails sent from our machine to as spam. The exact
>> same message sent using IPv4 within one minute of the IPv6 bounce is
>> accepted.
>> As there's no way to reach google mailops we had to remove IPv6 from our
>> mail machines and go back to IPv4 only for mail, which is sad.
>> Are we alone with this recent experience?

I have not experienced this since they enabled IPv6 on gmail but then I am small and I know others had problems initially.  Just tested using telnet from a random, but properly setup (DNS) IPv6 address which is not even an MX and it was fine.

However if they do bounce, you should get a good explanation with a link to a website in the reject/bounce, which last time I read (looking at other people’s bounces to help) was detailed enough to figure out what the problem could be. They did start to document things a while ago, which was really helpful for the wider community.

One important thing you might want to share (which might help people reading (lurking) maybe), is which set of servers (originating prefix and gmail server addresses) you are seeing this problem with;  it could very well be a specific cluster problem.

> They also reject any IPv6 transacted mail without valid reverse dns.

It might be a broad claim but I might be partially responsibility for that;  at least I mentioned it to them at one point that all Spam I up to that point had gotten over IPv6 had not reverse mapping 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 ->   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.


Bjoern A. Zeeb             "Come on. Learn, goddamn it.", WarGames, 1983

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