Hey there, just bought a new .app domain with Office365 (email essentials). Unfortunately, attempting to log into the ECP redirects to a blank page, and I get stuck in an OAuth2 loop when trying to use Outlook (I can access the Microsoft Office365 home page, but no apps nor email).
Neither Thunderbird (Linux) nor Mail (Windows 10) are able to connect.
Tried using the default settings GoDaddy suggested during setup, and then just retried recently with this configuration:
Re: Redirect loop attempting to use Office365 email
Got the issue resolved, but not entirely sure what caused it in the end.
A few things I had done that Microsoft probably didn't like: I used two underscores for the first and last name (I like privacy. Boo.) and probably bounced my logins for that reason.
I had used a rando name for my admin e-mail account rather than admin, postmaster, etc. I ended up deleting this account.
I'm also not entirely sure what GoDaddy had recommended go into the DNS records was what Microsoft really wanted. My final configuration ended up being a mix between what the MSDN article recommends, what GoDaddy autofills, and what GoDaddy recommends during initial setup.
That being said, since the error boundary was purely within Microsoft's Office365 splash -> Outlook product transition, I'm pretty sure the real issue was the first name and last name I provided, or the oddly named admin account.
Either way, if anyone finds this post in a Google search 10 years from now, hope it helps!