Hello, can you confirm if you are accessing your mailbox only through a browser and not any mail apps?
Open Outlook on the web, go to Settings, then Mail, then Sync email, and check if any connected accounts or forwarding is enabled, turn off forwarding and remove any connected accounts you do not recognize, then save. After that, go to Settings, then General, then Storage and clear up space if the mailbox is near limit, then sign out and back in. This will stop messages being redirected and ensure new emails deliver properly to your inbox.