Microsoft Account Errors

How to Change Microsoft 365 Admin Accounts to a Custom Domain

Huma Ashraf Ch Oct 9, 2026 869 views

Question details

The user needs to update the username and primary email address of Microsoft 365 administrator accounts, migrating them from the default tenant.onmicrosoft.com domain to a newly added custom domain.

Change Microsoft 365 Admin Accounts to a Custom Domain

Product: Microsoft 365 Admin Center
Device & OS: not provided
Scenario: Updating administrator account credentials after successfully linking a custom domain to the Microsoft 365 organization tenant.
Observed behavior: The admin accounts are currently operating on the default tenant.onmicrosoft.com domain and need to be transitioned to the organization's custom domain for unified branding and login.

Before you start

Ensure your custom domain is already successfully added, verified, and configured in the Microsoft 365 admin center before attempting to update administrator usernames.

Solution 1Recommended

Update Admin Account Domain in Microsoft 365 Admin Center

Use the Active Users management section in the admin center to manually switch the primary email and username of each administrator to the custom domain.

It is highly recommended to change administrator accounts one at a time. After changing one account, log out and log back in to confirm the new credentials work perfectly before proceeding to the next admin account. This practice ensures you do not accidentally lock yourself out of the tenant if there is a domain configuration issue.

Sign in to Microsoft 365 admin center

Navigate to the Microsoft 365 admin center using an account with Global Administrator privileges.

Navigate to Active users

On the left navigation menu, click on 'Users' and then select 'Active users'.

Select the admin account

Find and click on the administrator account you want to update. A user properties pane will slide out on the right side of the screen.

Manage username and email

In the Account tab, select the 'Manage username and email' option. Edit the primary email address and username by selecting your newly added custom domain from the drop-down list.

Save and verify

Click 'Save changes'. Log out and sign back in using the new custom domain email address to ensure it works before updating the remaining administrator accounts.

Update Admin Account Domain in Microsoft 365 Admin Center

Important Safeguard: Always keep at least one Global Admin account on the default domain untouched until you have successfully verified access with the newly updated custom domain accounts.

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Frequently Asked Questions

Why do I still see the onmicrosoft.com domain after adding my custom domain?

Adding a custom domain to your tenant does not automatically update existing users. You must manually change the primary email address and username for each user and administrator account to the new custom domain via the Active users section.

Will changing the primary email address affect my administrator access permissions?

No, your permissions and assigned roles remain exactly the same. Only your login ID and primary email will change, meaning you must use the new custom domain email address to sign in to the Microsoft 365 admin center moving forward.

What happens to the old onmicrosoft.com email address after the change?

When you change the primary email to a custom domain, the old onmicrosoft.com address is automatically retained as an alias (proxy address). You will still receive any emails sent to the original onmicrosoft.com address.

Can I change multiple administrator accounts at the same time to save time?

While bulk edits are possible for standard users, it is strongly advised to change administrator accounts one at a time. This ensures you do not lose tenant access if a configuration or propagation error occurs with the newly assigned domain.

Login & Account Issues