Most every bit of online exchange and O365 (+the ever-changing, ever-growing stack of MS policy/admin/security panels) is overkill for 10-20 users who need mail, Outlook, Word, Excel (no substitutions).

It's a massive hydra and it's most dependable output is onerous requirements. And the more of those we heap upon light duty users, the more reasonable it becomes to circumvent them.

In this scenario Winauth is how we placate the unreasonable overlord.