I like everything about Fastmail, but they're Australian and Australia seems to be one of the worst jurisdictions when it comes to data privacy. See this thread: https://news.ycombinator.com/item?id=18654434

Absolutely not. Fastmail is an Australian company and is subject to one of the most intrusive digital surveillance requirements in the Western world. And thanks to the Five Eyes framework, easily shared among intelligence agencies.

They do not compete on Privacy at all in my opinion. So then the choice comes down to price, features and economic viability of the organisation. I think price and features they are on par with Office 365, well at least for individuals not for enterprises.

But in terms economic longevity I think Microsoft wins hands down. Fastmail might be days away from bankruptcy, none of us would know as it is private company. I would rather have my personal email, that is the glue to modern life, with a Trillion dollar company than with a relatively new minnow.

I was going to recommend Fastmail as well. I'm a paying customer and very happy with it.

That does not answer his question, whether Office365 is better for privacy or not.