Gmail blocks my mailserver, I recently discovered it’s the lack of ipv6 that causes it.
Please provide citations if you’re going to speak so factually.
That's fair. I don't really have handy citations. I just know this stuff from working in email deliverability for a long time. I guess you can choose to believe me or not.
A mailserver was blocked by Gmail until I disabled IPv6 on it.
I just wish gmail had tech support so I could resolve this directly instead of flailing about trying random obscure solutions.
I decided I'd need to configure Exim4 to issue a different EHLO name depending on whether it's connecting over IPv4 or IPv6, and then triple check (with tests) that reverse DNS unambiguously matched in each case.
But as deliverability was the priority, disabling IPv6 seemed lower risk than fiddling with config, seeing it work, then finding out a few weeks later that it introduced another "Google mystery factor". Reviewing that is on the todo list somewhere, very low priority.