Dear Mario Blaum,
Welcome to Microsoft Community.
You can use this email address to send a test email to itself to check if it can be received in Inbox.
If you can't receive the email, check if there is a bounced email which has an undeliverable reason in it.
Also check if there are any forwarding or rule settings in the account that cause the server to reject other emails.

If you have recently changed your password for your Microsoft email account, please log out of your account in the upper right corner and log back in.
If none of the above methods solved your problem, please let me know the steps you tried. You can also seek help from online technical support, they may have other solutions: Contact - Microsoft Support
- Log in to another available Microsoft account (Make sure you sign in with your personal Microsoft account, not your work and school account, or you won't see option 3、4、5).
- Enter Outlook to search and Click" contact Support" at the bottom of the page.
- Under Products & Services, select "Microsoft 365 and Office".
- Under Categories, select " Outlook " and click Confirm.
- Click "Chat with a support agent in your web browser".
Best Regards,
Lucas Li – MSFT | Microsoft Community Support Specialist