

I don’t know the specifics of being a paid Exchange customer.
From my experience, I had to switch three servers. Domain and IP reputation seem to mean a LOT to Microsoft. You can’t be on a blacklist. There are blacklists in which you can request to be removed from - Microsoft doesn’t care.
Also, without setting up all the stuff you didn’t need to do 10 years ago, Microsoft also silently sends your email into the ether: DKIM, DMARC, SPF…
It’s infuriating, especially since they run a lot of the enterprise email hosting.
But think of the shareholder value lost if we invest in that!