Follow the instructions provided in this link for compromised accounts;
https://support.microsoft.com/account-billing/how-to-recover-a-hacked-or-compromised-microsoft-account-24ca907d-bcdf-a44b-4656-47f0cd89c245
Also, open the email from the Outlook website.
Click on the gear in the upper right corner.
Go to the Forwarding & IMAP, check if you have any settings you don't know about, and remove.
Go to your account settings https://account.live.com/proofs/manage/ click "Sign out of all locations."
Change your password and enable 2FA.
This process will take 24 hours to complete, after which you should stop receiving drafts.