Configuring preferences and options in Outlook.com
Apparently it's a big M$ is working on.
Tuesday May 26th they should have a fix for it.
Were you find this information?
The support guided me to the business support:
Do not think, that they can help...
Any one asked for a refund or something? for me key feature is missing...
btw. have the same 500 erros:
https://outlook.live.com/ows/api/v1/PremiumDomain
https://outlook.live.com/ows/api/beta/PremiumUser
.....