Microsoft Account Errors

Why Microsoft 365 Users Receive an onmicrosoft.com Alias & How to Manage It

Algirdas Jasaitis Oct 21, 2026 869 views

Question details

Administrators and users want to understand why a default onmicrosoft.com alias is automatically generated for every new user account and how to handle it properly.

Understanding the Default onmicrosoft.com Alias in Microsoft 365

Product: Microsoft 365
Device & OS: not provided
Scenario: Creating new user accounts or managing existing users within a Microsoft 365 organizational tenant.
Observed behavior: An alias utilizing the tenant's onmicrosoft.com domain is automatically attached to the user account. Even if deleted, it frequently regenerates or is flagged as an undeletable system requirement.

Before you start

Ensure you are logged into the Microsoft 365 Admin Center with Global Administrator or User Administrator privileges to view and modify user domain configurations.

Solution 1Recommended

Configure Your Custom Domain as Primary Instead of Deleting the Alias

Since the onmicrosoft.com alias is required by Microsoft for backend identity routing and service integrity, the best approach is to retain it while ensuring your preferred custom domain is set as the primary address.

Microsoft 365 utilizes the onmicrosoft.com address as a permanent, reliable routing destination for internal services like SharePoint, Teams, and identity management. Attempting to permanently disable or delete this alias is unsupported and will typically result in the system automatically recreating it.

To prevent this alias from causing administrative or visual issues, simply ensure that your organization's custom domain is established as the primary sender and receiver address.

Access the Admin Center

Navigate to admin.microsoft.com and log in with your administrator credentials.

Navigate to Active Users

In the left-hand navigation menu, expand the 'Users' dropdown and click on 'Active users'.

Open User Properties

Click on the display name of the user you want to modify to open their account properties panel on the right side.

Manage Email Aliases

Under the 'Account' tab, locate the 'Username and email' section and click the 'Manage username and email' link.

Set the Primary Domain

Locate your preferred custom domain address in the list. Click the 'More actions' (three dots) icon next to it and select 'Change to primary email'. Leave the onmicrosoft.com address in the list as a secondary alias.

Configure Your Custom Domain as Primary Instead of Deleting the Alias

Invisible to Recipients: As long as your custom domain is correctly set as the primary address, the onmicrosoft.com alias remains completely invisible to external recipients when sending or receiving emails.

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Frequently Asked Questions

Can I permanently delete the fallback onmicrosoft.com domain from my tenant?

No, the initial onmicrosoft.com domain is permanently tied to your Microsoft 365 tenant for internal backend routing, subscription management, and Azure Active Directory purposes. It cannot be removed or renamed.

Will external contacts see the onmicrosoft.com email address when users send emails?

Not if you have correctly configured a custom domain. When a user sends an email, the recipient will only see the address configured as their 'Primary email address' in the admin center.

What happens if I try to force delete the onmicrosoft.com alias via PowerShell?

While you might be able to temporarily remove it using PowerShell scripts, Microsoft's backend synchronization processes will automatically recreate the alias during the next sync cycle because it is required for service integrity.

Do I need the onmicrosoft.com alias to use Microsoft Teams or SharePoint?

Yes, these underlying services rely heavily on the default tenant routing domain behind the scenes for user identity mapping, file sharing, and internal system communication.

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