Managing personal Outlook.com account settings, security, and privacy
If that address is appearing with messages from trusted senders, check for mailbox tampering first.
- In Outlook.com on a computer, open Settings.
- Go to Mail > Rules and delete any rule that was not created intentionally.
- Check Forwarding and IMAP and remove any forwarding or transfer settings that are not recognized.
- Go to the Microsoft account site, open Your info > Sign-in preferences, and review aliases. Remove any alias that is unfamiliar.
- Open Security and review Manage how I sign in or Advanced security options. Remove any unrecognized verification email address if it appears there.
- Review recent sign-in activity at the recent activity page to check for unusual access.
- Change the account password and make sure two-step verification is enabled.
If the unfamiliar address appears only during verification and is not listed in account settings, use the Microsoft Sign-in helper.
For suspicious or spoofed messages in Outlook, be cautious with messages that show an unverified sender or a different actual sender address than the From address. In Outlook and the new Outlook on the web, hovering over the sender can show the actual email address.
For identity-theft exposure, Microsoft Defender identity theft monitoring can help determine whether an email address was exposed in a breach.
The available guidance does not provide a way to identify exactly who owns that address.