Fastmail is very good and has been running for 24 years, with good deliverability. Migadu I hear is good. There's quite a few email providers that aren't Microsoft or Google that have their shit together.
Yeah, fastmail is pretty close to office 365. As long as you're not dependent on Aszure for other components. I suggest businesses think about migrating away from 03 65 because this problem will probably get worse in the future, since Microsoft is either too big, or not able to secure their own security implementation.
