Outlook keeps asking for login credentials during setup
Answer:

there seems to be a bug if you use outlook accounts which are not ending on outlook.com.

If you go to https:\login.live.com you can login with other credentials.
There is a menü "Your Informations" where you can edit the email or telefon alias.
In this menü you can create an outlook.com alias.

With this outlook.com alias login from Outlook on outlook mobile to Outlook.com works and contacts can be retrieved.