I would like to add Microsoft Office 365, most of you would like access to the Office applications. If not, that is fine as you can still pay less. You also get Azure Active Directory included for free, which you can use for single sign on applications you have(up to 10 applications).

I am founder for a new startup and we decided to go for Office 365 as our email service because it just made most sense for our business. And those who knows me, know that I prefer to avoid Microsoft solutions most of the time.