Hello Natalie,
To stop this completely, you’ll need to do a thorough cleanup, Sign in to Outlook Web and check Settings → Mail → Rules for any suspicious rules (like the “Demon” one you found) and delete them. Also check Mail → Forwarding and remove any unknown forwarding addresses. Next, go to Microsoft Account Security and use Sign out everywhere to kill all active sessions.
Then visit Manage App Permissions and revoke any apps you don’t recognize, hackers often use these to maintain access. If you have Microsoft 365 admin access, review Exchange Admin Center → Mail Flow → Rules and run PowerShell commands like Get-InboxRule -Mailbox youraddress@example.com to find and remove hidden rules.
Finally, reset your password again, keep MFA enabled, and monitor sign-in logs for suspicious activity. Microsoft also recommends checking for connectors or add-ins that might have been installed.
This might help