When setting up a Microsoft 365 tenant, it comes with an initial subdomain that ends with ‘.onmicrosoft.com.’ This is known as the fallback domain and has implications for all your services and naming conventions, including user UPNs and SharePoint site links. Many customers realize the importance of the fallback domain and its impact on services quite late. Fallback domains are generally created by entering a random name during the installation phase therefore, there may be a need to add a new .onmicrosoft.com domain. Here’s a step-by-step guide for adding a new .onmicrosoft.com domain:
Step 1: Sign in to Microsoft 365 Admin Center
Go to the Microsoft 365 Admin Center ( admin.microsoft.com ) and sign in with your administrator account.
Step 2: Access the Domains Section
In the Admin Center, go to “Settings” and then click on “Domains.”
Step 3: Add a new .onmicrosoft.com domain
Find your existing .onmicrosoft.com domain in the list. In this example tayfntek.onmicrosoft.com
Click on the domain and then click the “Add onmicrosoft.com domain (preview)” button at the bottom right.
Follow the on-screen instructions to complete the setup
Once verified, click “Finish” or a similar option to complete the domain setup.
Congratulations!
