[beagle3]

Google effectively killfiled a domain I run. It took me a few months to figure out, but about 95% of emails sent to @gmail.com or g-suite hosted addresses from that domain (which were, overall ~20% of emails sent), got into a spam folder.

No recourse, no one to talk to; my solution was to switch from a small but reputable ISP I had used for 17 years (and which never had a single spam complaint or blacklist entry in any list I can read) to fastmail for that domain; because Google decided they didn't like something about that setup; already spent a couple of work days no one was paying for to troubleshoot and eventually gave up.

Google+Microsoft+FastMail likely cover 95% of your recipients. If they don't like you, you're going to have a very hard time reaching people.