Sometimes when I send from my server, I get the following response from Gmail (IP masked by me)
: host aspmx.l.google.com[2a00:1450:4013:c00::1a] said: 550-5.7.1 [2a01:**:**:**::2 12] Our system has detected that this 550-5.7.1 message is likely unsolicited mail. To reduce the amount of spam sent 550-5.7.1 to Gmail, this message has been blocked. Please visit 550-5.7.1 http://support.google.com/mail/bin/answer.py?hl=en&answer=188131 for 550 5.7.1 more information. hm5si113822760wjb.117 - gsmtp (in reply to end of DATA command)
Some people recommended to disable IPv6 for Gmail. But google seems to miss an IPv6 PTR entry in the DNS. I found some help on this, but all this stuff is a bit above my head.
To my understanding I just have to create a PTR record for instance with the help of this tool and add that to my DNS record.
Is it that simple?