Postfix trouble sending to gmail

A while I ago my server at hetzner started having trouble sending mail to gmail accounts so I asked the world if there was someone out there with the same problem. Someone told me gmail has some random problems using ipv6 but mine didn’t looked very random.

The message I got in return said:[2a00:1450:4001:c02::1b] said: 550-5.7.1
    [2a01:4f8:d13:3c03::C0:FF:EE] Our system has detected an unusual rate
    550-5.7.1 of unsolicited mail originating from your IP address. To protect
    our 550-5.7.1 users from spam, mail sent from your IP address has been
    blocked. 550-5.7.1 Please visit to review 550 5.7.1 our Bulk
    Email Senders Guidelines. v46si12358een.61 - gsmtp (in reply to end of DATA

So I started searching to find out what went wrong. First I expected to find some strange processes on my system but I couldn’t find any I didn’t wanted to start. Even my postfix logging didn’t showed anything unusual so I started wondering if gmail wasn’t wrong about their message.  But even the click here for more help brought me back to the startpage.

To be really really sure their wasn’t anything wrong, I did two thing:

  • I started tcpdump to log all traffic going out on ipv6 on smtp
  • I waited, expecting gmail to finally allow my server sending mail to their server

But it didn’t help: there was no strange traffic and gmail still didn’t allow me. On the page gmail was pointing to in their error message they give you some hints when sending out bulk mail. Although I wasn’t doing naughty stuff, I checked their points.
One of the things they tell is Keep valid reverse DNS records so I verified mine. Finally I discovered my AAAA record wasn’t correct (anymore?). After correcting this and waiting for DNS propagation, I could finally send messages again to gmail accounts. So I’m a happy penguin again.


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