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

[Darren Pilgrim]

On 8/22/2014 7:32 AM, Lorenzo Colitti wrote:
> Note that from the text it sounds like SPF / DKIM is not strictly
> required, but it looks like a PTR record is a hard requirement.

PTRs are a hard requirement, yes.  That's not a problem.  All places 
where you can run a legitimate MX will have working reverse DNS and 
nearly all will facilitate FCRDNS.

The problem is Google ignores the fact you must not hard fail on DNS. 
Even if the response is NXDOMAIN, the most you can do is soft bounce 
because you can not know why you didn't get an RR.  Gmail hard bounces 
on such errors even though doing so accomplishes nothing you could 
consider an anti-spam countermeasure.

I get relay failure to gmail at least once every day.  It is always the 
same thing: gmail's server didn't get a response to the PTR lookup and 
5xx'd the mail.  I've even seen mail to the same server succeed mere 
seconds later.  Google has an internal reliability problem and a policy 
that pushes the cost out to those with no power to fix it.

"Please resend the email and let me know if it fails again" is not what 
my users want to hear, but it's the only answer that works.
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