Have you ever tried to use it? Because I fought for about 2 months with both Google and Microsoft, trying to self-host my mail server, to no success. The only answer was amongst the lines 'your server has not enough reputation'. Even though perfectly configured, DKIM, DMARC, etc. Now imagine a business not being able to send a message to anyone hosted on Gmail or Outlook, probably 80-90 percents of the companies out there.
I feel you. I had my email on OVH for a while, but they handle abuse so bad that Apple just blanketed banned the /17 my IP was in. And I was lucky that Apple actually answered my emails and explained why I was banned. I doubt Microsoft and Google would give you any useful information.
