Change original MS 365 Organizer username

Hi Ronald Tang,

Based on my research, in Microsoft 365 for business, the “original login username” you’re referring to is actually the User Principal Name (UPN**)**, which is the account’s primary sign‑in name. This can be updated by an administrator and does not require creating a new account or moving your subscription.

If you have Global Administrator access, you can update the sign‑in name directly from the Microsoft 365 Admin Center:

1. Go to Microsoft 365 Admin Center
2. Navigate to Users > Active users
3. Select the affected user account
4. Click Manage username and email
5. Update the User name / Sign‑in name (UPN) to the new email address you want to use

Important notes:

• The new email domain must already be added and verified in your Microsoft 365 tenant.
• Changing the UPN does not remove your mailbox, OneDrive data, or licenses.
• Changing your Internet service provider does not automatically require a username change. This is an identity management setting within Microsoft 365.

You can review the official Microsoft documentation here:

• Change a user name and email address
• Add a custom domain to Microsoft 365

I hope this information is helpful. If anything is unclear, or if I’ve misunderstood your scenario, please feel free to let me know and I’ll be happy to assist further.

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