DKIM, DMARC, SPF, rDNS/PTR, EHLO... all correct and verified in the email "original source," BY GOOGLE. Still goes to SPAM folder because **** you, apparently. I hate Google.
Probably bad place to ask but.
Self hosting email is complicated only for sending mails or for receiving mail it's also hard?
Depending on what you want to do you might not need to actually send any mail.
Also, the anti-spam rules do also apply if you are answering a mail, I suppose it does as a response envelopement doesn't have any evidence that it's an actual response. But I have no experience self hosting email.