[j_s]

From the fine article he linked: SPF, DKIM and DMARC are all domain verification systems for validating e-mail’s origin to prevent spam. I have all three records set in DNS records for all the domains I send e-mail from, verified they were correct using testing tools, and I still get flagged as spam.

[codezero]

Google uses a lot of signals. The article above is on http, I saw a drop in spam flagging when the web host on my email domain was https only.