Ok, this may be a bit of a weird issue.
I setup Mailcow recently and moved several domains from Mail-in-a-Box over. Everything seems to work fine except email delivery from gmail. E.g. the sign up email from this forum arrives fine, as do most other emails. But the tests mails I sent from an unrelated @gmail.com address do not arrive. I can send email to my @gmail, it arrives nicely in the inbox, but reply emails do not reach me - at all.
There’s no connections from google servers to my Postfix, so they’re not even trying.
MX is setup correctly, as other providers, like Microsoft, can deliver mail just fine within seconds.
What’s the best way to further troubleshoot this? I’m guessing Google is verifying something they think is not okay.