Hi Torgeb,
From the information provided, the custom domain added to Office 365 is a subdomain, instead of top-level domain. Moreover, using subdomain with an Office 365 for Small Business (Plan P1) account is not supported currently.
Please add a top-level domain, such as domain.no, to the Office 365 Plan P1 account to use the custom domain with Office 365 services.
Thanks,
Claud