Gotta be willing to suffer losses. The only way we can stop this from happening is if enough people stop using gmail so google actually can't get away with whitelisting email domains. Doing it naively, game theory is not in our favor, like with climate destabilization, but making it cool (like OP does) might actually help?

You can start by having your email server “hide” behind gmail or friends.

I’d be interested to hear a specific expansion on this point (“hide” how? etc). I think the gp raises some valid concerns.

Have your Gmail account pull emails from your in box, have Gmail send as if from your email address.

Exactly this - in "Exchange" terms they called it something like "smart host" if I remember. But basically you use a major provider to do the final "connect to the internet at large" but everything is on your machine and you could change your outbound routing at anytime.

Such an obvious solution when you point it out that way. Thank you!

One compromise that I can recommend is hosting the Email server yourself for incoming mail, but using an external SMTP relay such as SendGrid or SMTP2GO to send outgoing email. That way you never have to worry about your emails being blocked due to some misconfigured setting. Switching SMTP relay provider is easy so vendor lock-in is no issue.

Also, those services are mostly intended for broadcasting mass spam mails for better or worse, so for personal use their free tiers are almost too good to be true.