I can't add another new alias email to my account

Several Microsoft account rules can prevent adding a new alias, even if the email address looks “available” as a new account.

Key limitations and checks:

1. Alias cannot already be a Microsoft account

• An alias cannot be added if that email address is already associated with another Microsoft account (including old or unused ones).
• Existing @hotmail.com, @live.com, @outlook.com, and @msn.com addresses cannot be added as aliases to another Microsoft account.

2. No account merging or recycling

• Microsoft does not support merging two Microsoft accounts.
• Outlook.com addresses are not recycled as aliases. If an Outlook.com address already belongs to a Microsoft account, it cannot be moved or reused as an alias on a different account, even if that other account is closed.

3. Organization or domain restrictions

• If trying to add a work/school address, the organization may block using that domain as an alias.
• Aliases cannot be used to share information between two Microsoft accounts.

4. Supported way to add an alias To add a valid alias to a personal Outlook/Microsoft account:
5. Go to the Microsoft account “how you sign in” page (for example via Edit account info or Manage how you sign in to Microsoft).
6. Select Add email.
7. Either:
   • Create a new Outlook.com email address and add it as an alias, or
   • Add a non-Microsoft email (such as gmail.com or yahoo.com) that is not already tied to another Microsoft account.
8. Complete any verification steps.

If the address being added violates any of the rules above (already a Microsoft account, existing Outlook.com/MSN/Hotmail/Live address, or restricted domain), the add-alias operation will fail, even if the address appears “available” as a brand-new account.

References:

• Add or remove an email alias in Outlook.com
• "Something went wrong" with error ADDriverStoreAccessNonLocalException
• How to add an email address or phone number to your Microsoft account
• How to add an existing outlook.com account to my existing microsoft account? - Microsoft Q&A
• MSN email issues - Microsoft Q&A
• I realize I have 2 different accounts. How do I combine the 2? - Microsoft Q&A