We run everyting in the native Samsung App for our Android clients.

I run my outlook.com account in outlook app. Nothing else.

eM Client now has a mobile app. I've used it and it's very nice. They're continuing development of it as well, and it will soon include calendars, tasks, contacts, and notes. May be worth a look: https://www.emclient.com/mobile-features

Nine is such a great app!

The only big problem is getting customers to digest the cost of the app.

Nobody wants to pay to read their e-mail on their smartphone.

I've been using the em client app with EWS for a few months ever since samsung mail started causing issues with teslas messaging integration. It has been a very solid email client. I have not had any issues with it. I just wish that we could get calendars but they are still developing that. To get around that I added my mail account as an exchange account to samsung calendars and that works fine.