[tyingq]

It looks like they are just trying to limit abuse during a rollout. Forcing a "work" or "school" email to try and hold back anonymous signups.

You can pre check an email with their embedded ajax call:

https://flow.microsoft.com/providers/Internal.User/users/use...

If the JSON comes back with "consumerDomain":true, then it won't allow the signup.

They don't seem to be catching all free email services. At the moment, it appears you could sign up for a free Yandex email and get signed up for Flow:

https://flow.microsoft.com/providers/Internal.User/users/som...