I went to sign in with my mobile number and it sent an email to an unknown email address

Hi, I'm John! I will help you with this.

That usually means the mobile number is already linked to a Microsoft account.

To help narrow down the issue:

1. Are you trying to sign in or create a new account?
2. Did you ever use that phone number before with Microsoft (Skype, Outlook, Xbox, etc.)?
3. Do you recognize any part of the masked email shown (like ***@domain.com)?

In the meantime, if you haven’t already already:

• Go to account recovery: https://account.live.com/username/recover
• Enter your mobile number and see what account shows up
• If you don’t recognize the email at all, do not try to access it

If it still points to an unknown email, it’s best to contact Microsoft support so they can check if your number was used by someone else.

Let me know what you see on the recovery page.

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This behavior usually means the mobile number is already associated with a different Microsoft account (as an alias or security info), so the sign-in system is sending a verification email to that account’s primary email address.

To secure the situation and correct the account association:

1. Check for unusual or unauthorized activity
   • Go to the Security basics page and sign in with the account you can access.
   • Select Review activity and check the Recent activity page for sign-ins or security changes you do not recognize.
   • If you see anything suspicious, mark it as This wasn’t me or Secure your account, and then change the password.
2. Verify which account the phone number belongs to
   • Phone numbers and email addresses used with Microsoft accounts are aliases and can be used to sign in.
   • If the sign-in flow shows an unknown email when using the phone number, that email is likely the primary alias of the account currently holding the number.
   • If that email truly does not belong to you, treat this as a potential account mix-up or security issue and proceed to secure your own account and remove that phone number from any account you control.
3. Fix or update your aliases and security info (for accounts you own)
   • Sign in to your Microsoft account’s “how you sign in” page via Edit account info.
   • Review the list of aliases (email addresses and phone numbers) associated with the account.
   • If your phone number is attached to the wrong alias or you no longer want it there, remove it and then:
     • Select Add phone number to attach it to the correct account.
   • Remember: all aliases on one account share the same password and can be used to sign in.
4. If you suspect someone else is using your phone number
   • Go to the Security basics page for your own Microsoft account and ensure your security info (phone, alternate email) is correct and up to date.
   • If you cannot sign in because the phone number is tied to an account you do not recognize, use the guided recovery tool for “forgotten email address or phone number” to locate the correct account and reclaim it if it is yours.
5. If the unknown email is definitely not yours
   • Do not try to access that email account.
   • Secure your own Microsoft account (change password, review recent activity, confirm security info).
   • Remove or change the phone number from any Microsoft account you control, then add it back only where you want it.

If sign-in is blocked due to unusual activity, follow the instructions on the sign-in screen to receive and enter a security code, or sign in from a trusted device or usual location as described in the unusual sign-in guidance.

References:

• What happens if there's an unusual sign-in to your account
• Help with "phone number is already used" in a Microsoft account
• How to add an email address or phone number to your Microsoft account