Thanks Google for your new IPv6 mail policy

The short version is: Fucking idiots!

Long version:
Google Mail introduced a new policy somewhere in August 2013 for receiving e-mail via IPv6. Earlier the policy was same for IPv4 and IPv6, but they decided to make Internet a better place by employing a much tighter policy for e-mail senders. Details can be found from their support pages.

For e-mail Authentication & Identification they state:

• Use a consistent IP address to send bulk mail.
• Keep valid reverse DNS records for the IP address(es) from which you send mail, pointing to your domain.
• Use the same address in the 'From:' header on every bulk mail you send.
• We also recommend publishing an SPF record
• We also recommend signing with DKIM. We do not authenticate DKIM using less than a 1024-bit key.
• The sending IP must have a PTR record (i.e., a reverse DNS of the sending IP) and it should match the IP obtained via the forward DNS resolution of the hostname specified in the PTR record. Otherwise, mail will be marked as spam or possibly rejected.
• The sending domain should pass either SPF check or DKIM check. Otherwise, mail might be marked as spam.

First: My server does not send bulk mail. It sends mail now an then. If the idiots label my box as a "bulk sender" (whatever that means), there is nothing I can do to help it.

Second: I already have done all of the above. I even checked my PTR-record twice. Yes, it is in the above list two times using different words.

Still, after jumping all the hoops, crossing all the Ts and dotting all the Is: they don't accept email from my box anymore. They dominate the universe, they set new policies, start to enforce them without notice and fail to provide any kind of support. At minimum a web page to fill in couple of fields to a form to test how they perceive your server and give a result what to fix. But no. They don't do that, they just stop to accept any email.

To provide matching words for their search engine, I post a log entry (wrapped to multiple lines) from my Postfix:

postfix/smtp[6803]: A82C94E6CE:
to=<my@sending.address.fi>,
orig_to=<the@recipient's.address.net>,
relay=aspmx.l.google.com[2a00:1450:4008:c01::1b]:25,
delay=0.76,
delays=0.04/0/0.35/0.37,
dsn=5.7.1,
status=bounced (host aspmx.l.google.com[2a00:1450:4008:c01::1b] said:
550-5.7.1 [2001:-my-IPv6-address-      16]
Our system has detected 550-5.7.1 that this message does not meet IPv6 sending guidelines regarding
PTR 550-5.7.1 records and authentication.
Please review 550-5.7.1 https://support.google.com/mail/?p=ipv6_authentication_error for more 550 5.7.1 information.
qc2si10501687bkb.307 - gsmtp (in reply to end of DATA command))

I'm not alone with my problem. Easily a number of people complaining about the same issue can be found: Gmail, why are you doing this to me? and Google, your IPv6-related email restrictions suck. Most people simply stop using IPv6 to deliver mail to Google. My choice is to fight to the bitter end.

While complaining the un-justified attitude I get from Google, I got a piece of advice: "Why don't you check what Google's DNS thinks of your setup?". I was like "WHAAT? What Google DNS?"

In fact there is a public DNS offered by Google. It is described in article Using Google Public DNS. I did use that to confirm that my DNS and reverse-DNS were set up correctly. I typed this into a BASH-shell:

# dig -x 2001:-my-IPv6-address- @2001:4860:4860::8888

It yielded correct results. There was nothing I could do to fix this issue more. As it turned out, I did not change anything but after a couple of days, they just seemed to like my DNS more and allowed my email to pass. Perhaps one of these days I'll write something similar to my open recursive DNS tester.

Idiots!