Friends, I did it. I managed to use my domain christian-gaeng.de with Microsoft 365 again. I hadn’t been able to do this since 2022. And do you know what the problem was?
I had my domain with GoDaddy, and I had also subscribed to Exchange Plan 1 through them at the time. When I then moved my domain to another provider, I assumed that this would also cut off all connections to M365. Far from it. A so-called “tenant” remained on GoDaddy’s servers, blocking any further use of M365.
Only now, three years later, did I find a competent Microsoft support employee who recognized the problem. Thank you, Microsoft.