I run an email domain for myself and three friends. I set it up 10+ years ago and originally it was for ~15 people. It's only personal email and no one uses it

I run an email domain for myself and three friends. I set it up 10+ years ago and originally it was for ~15 people. It's only personal email and no one uses it for marketing or anything even remotely shady. We setup DKIM and all of the similar best practices. In the last 6-12 months, we've had lots of issues with gmail marking our messages as spam for users we haven't emailed before. And what sucks about it is there's nothing you can do. People assume it's your fault for being weird and not using Gmail or outlook.com. And there's zero way to contact Google or submit information to convince them you're legitimate. I believe in an open, distributed internet. I don't think it's good that we're moving towards a world we're the core protocols that defined the internet are being replaced by proprietary versions controlled by a handful of trillion dollar companies.