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.
Don't take this as an endorsement as it's not really intended to be used for this purpose and I'm probably going to switch, but I've been using sendgrid for a few years as I was familiar with it from business use. I was using mandrill before that until they changed their pricing and some other things.
EDIT: also worth mentioning I have a grandfathered free plan.