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.
You can use MXToolbox to check for blacklists on your IP. If you find any, you can submit to each party to get removed. I've done this for a previous company and it was super easy.