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.
Self-hosting email is quite the undertaking... I don't have the energy to deal with it and just pay 10€/year for a hosting service.
Here's an informative (and funny) talk on why self-hosting email in its current state is probably a bad idea.