I run my own mail server and Google - for once - seems to play reasonably nice, it is Microsoft and Apple that are the harder cases, in part because they outsourced some of their vetting to third parties.
I've been mulling switching to Google or some other email provider for a long time and I still feel that this is the last bit of corporate independence that I'm willing to give up. Our mail is ours. I don't care of the counterparty is using gmail or whatever other flavor of cloud services they care for but running your own mail server should be a first test of whether or not you are an IT business or not.
It borders on the ridiculous to have to outsource something as essential and confidential to a commercial provider in another country who only entered the scene about a decade after us, especially because I see those commercial providers as the biggest part of the problem to begin with and this feels like rewarding them for their abusive behavior.
A snail mail analogy escapes me but it would involve sending your post all the way around the planet first before dropping it in the mailbox in the next town over, with some random elements for delivery or non-delivery thrown in for added amusement.
All this gives rise to some frustration on occasion, it is no fun to have your legitimate email classed as spam for reasons not under your control but so be it, I'll take that over giving up autonomy.
Google 'AMP' for email is yet another step in the wrong direction and I'm sure that it will get a lot worse before it will get better but at some point I'd hope that people will wake up to the fact that all this consolidation of power is a negative thing.