I can't change email address for logging in my Microsoft subscription account by another existing email at outlook.com, the email system recogised "This email address is already taken. Please try another.'

Hi @Trust customer 
Thank you for reaching out to the Microsoft Q&A forum  
I understand you're trying to use an existing email address as a login alias for your Microsoft subscription, and I'd be glad to help clarify why this is happening. 

Based on how Microsoft accounts are structured, you can't add an existing email address as an alias. The system gives you the "This email address is already taken" message because the email you're trying to add is already its own active Microsoft account. Aliases are intended for alternate email addresses that aren't currently linked to any other account. 

Reference: Add or remove an email alias in Outlook.com - Microsoft Support 

Unfortunately, subscriptions are also tied to the original email address used to sign up. If you'd like to use a different email address as the primary one for your subscription, the process involves: 

• Cancel the current subscription, 
• Request a refund (if applicable), 
• Then re-subscribe using the account you wish to have as the primary one. 

I know this might not be the simple answer you were hoping for, and I sincerely apologize for any inconvenience. I hope this explanation helps you understand the process and find the best way forward. 

Thank you again for your cooperation and understanding. 

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