Using New Outlook on Windows for personal email, calendar, and contact management
Hi. I'm Brian and I'll try to help.
The symptoms you describe could be due to a compromised account where the hacker added forwarding or a forwarding rule to your mailbox. Have you checked for that? Select Settings>Mail>Rules and look for any rules you did not add. Also check https://outlook.live.com/mail/options/mail/forwarding for a forwarding address you did not add. You will likely have to log in a second time for that. Also, check https://account.live.com/activity for any successful logins you do not recognize.