I disagree - Outlook is a walled garden of closed standards, and it makes users vulnerable to the whims of Microsoft or dependent entirely on their office ecosystem.

The recent outlook hack with senior accounts hacked and only being informed by Microsoft of the hack 1 year later is a good example.

Outlook is superficially good but essentially big businesses and organisations are locked in to a proprietary system for email and calendars and entirely reliant on Microsoft to keep their data secure.

I'm actually surprised Antitrust laws aren't used to break up the Office 365 monopoly. Only the teams integration is being challenged but the tight integration between Outlook, Office and OneDrive is monopolistic. Other services could integrate in the same way if Microsoft was forced to open up its APIs, which would be good for competition and customers.

At the moment you pretty much have to go all in with Office or forgo major integration benefits if you want to use different cloud or mail services. Why do you need 1 single provider for office software, mail and cloud storage?