I think of our company as an "indie" startup and we use Office365 for email. There are a bunch of things that I hate about it but what are the plausible alternatives? Before we moved to O365 85%+ of our emails landed in spam folders.
There's google, which is less infuriating to use than microsoft stuff from what I've heard. Microsoft, google and yahoo regularly block or delay mails from independents[1].
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.
Sometimes you get a bad roll of the dice when you choose a lesser known email provider and you start with worse than average reputation. Can never go wrong with Gsuite, O365, etc.
This is what I used to do (and what my father still does). Essentially if you don't have 20+ years of history you appear to be doomed on this. Adding DKIM / SPF even configured correctly didn't seem to do much good.
