Hi John Burlison,
Thank you for reaching out to Microsoft Q&A forum.
To help narrow this down more accurately, could you please confirm the following:
1. What type of account are you using?
- Is this a personal Microsoft account (Outlook.com / Hotmail / Live / MSN), or a work or school account (Microsoft 365)?
2. How are you trying to add the alias?
- Creating a new Outlook.com address, or
- Adding an existing email address (for example, Gmail or a custom domain email)?
Note: @outlook.com / @hotmail.com / @live.com / @msn.com addresses can’t be added as aliases, and an alias can’t already be linked to another Microsoft account.
3. Is passwordless sign‑in enabled on your Microsoft account?
4. If this is a personal account, please try again using an InPrivate/Incognito window, a different browser, and if possible a different network (and turn off any VPN if you’re using one), then let me know whether the same error still occurs.
Based on what you confirm, I’ll guide you through the appropriate next steps.
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