Send & Receive Issues

How to Use a Custom Domain Instead of onmicrosoft.com in Microsoft 365

Phi Hung Vo Oct 13, 2026 870 views

Question details

The user wants to set up and use a custom domain for Microsoft 365 emails and Teams invites, replacing the default onmicrosoft.com address.

How to Use a Custom Domain Instead of onmicrosoft.com in Microsoft 365

Product: Microsoft 365 / Outlook
Device & OS: not provided
Scenario: Configuring a professional custom domain for email communication and Teams while keeping the default domain in the background.
Observed behavior: Emails sent to the custom domain are routing to the onmicrosoft.com inbox, and duplicate inboxes appear in the Outlook client.

Before you start

Ensure you have global admin access to the Microsoft 365 admin center and access to your domain registrar's DNS settings.

Solution 1Recommended

Set Your Custom Domain as the Primary Email Address

Configure your custom domain to act as the primary sending and receiving address instead of creating a separate mailbox.

Access Active Users

Log in to the Microsoft 365 admin center and navigate to the 'Users' > 'Active users' section from the left-hand sidebar.

Manage Username and Email

Select the user account you want to modify. In the panel that opens, click on 'Manage username and email' located under the Account tab.

Change Primary Address

Add your custom domain as an alias if it isn't already listed. Once added, click the 'Change to primary' option next to the custom domain address.

Save Configuration

Click 'Save changes'. This ensures that all outgoing emails and Teams invitations will now display your custom domain instead of the onmicrosoft.com address.

Set Your Custom Domain as the Primary Email Address

DNS Propagation Delay: Changes to your domain and email addresses may take up to 24 hours to fully propagate across all Microsoft services.

Solution 2

Remove Duplicate Account Profiles in Outlook

Resolve the issue of seeing both the custom domain and onmicrosoft.com inboxes in your Outlook desktop app.

Free Microsoft Office alternative

Discover WPS Office: A Powerful and Free Alternative to Microsoft 365

While email domain configurations require Microsoft 365's admin center, you don't need expensive subscriptions for your daily document productivity. WPS Office offers a free, lightweight, and highly compatible alternative to Microsoft Word, Excel, and PowerPoint.

Fully compatible with Microsoft Office formats including .docx, .xlsx, and .pptx.Lightweight installation with rapid startup times for improved device performance.Familiar tabbed user interface, ensuring a seamless migration with zero learning curve.Built-in PDF editing, conversion, and annotation capabilities at no extra cost.

microsoft office alternative - wps office

Frequently Asked Questions

Why do messages sent to my custom domain go to the onmicrosoft.com inbox?

This happens when the custom domain is added as an alias rather than the primary SMTP address. You need to change the primary email address in the Microsoft 365 admin center so that the custom domain becomes the default inbox.

Can I completely delete the onmicrosoft.com domain?

No, Microsoft 365 requires the initial onmicrosoft.com domain for background routing and backend subscription management. However, you can effectively hide it from users and recipients by setting a custom domain as the primary address.

Why am I getting bounce-back messages after changing my domain?

Bounce-back messages often occur due to DNS propagation delays. When you update your MX and TXT records with your domain registrar, it can take anywhere from a few hours to 72 hours for the new DNS records to fully update globally across all email servers.

How do I ensure Teams invitations use my new custom domain?

Once you successfully set the custom domain as the primary email address (SMTP) for a user in the Microsoft 365 admin center, Microsoft Teams will automatically start using this address for all outgoing meeting invitations.

Outlook & Email Problems