Add your custom domain name to your tenant

Microsoft Entra tenants come with an initial domain name like, domainname.onmicrosoft.com. You can’t change or delete the initial domain name, but you can add your organization’s name to the initial domain. By adding your custom domain name, you can then add user names that are familiar to your users, such as [email protected].
Add your custom domain name

After you create your directory, you can add your custom domain name.

1. Sign in to the Microsoft Entra admin center as at least a Domain Name Administrator.
2. Browse to Identity > Settings > Domain names > Add custom domain.

3.In Custom domain name, enter your organization’s domain, in this example, contoso.com. Select Add domain.

4.The unverified domain is added. The contoso.com page appears showing the DNS information needed to validate your domain ownership. Save this information.

Add your DNS information to the domain registrar

Follow these steps:

1. After you add your custom domain name, you must return to your domain registrar and add the DNS information from your copied from the previous step. Creating this TXT or MX record for your domain verifies ownership of your domain name.
2. Go back to your domain registrar and create a new TXT or MX record for your domain based on your copied DNS information. Set the time to live (TTL) to 3600 seconds (60 minutes), and then save the record.

Verify your custom domain name

After you register your custom domain name, make sure it’s valid in Microsoft Entra. The propagation time can be instantaneous or it can take a few days, depending on your domain registrar.

To verify your custom domain name, follow these steps:

1. Sign in to the Microsoft Entra admin center as at least a Domain Name Administrator.
2. Browse to Identity > Settings > Domain names.
3. In Custom domain names, select the custom domain name. In this example, select contoso.com.

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4.On the contoso.com page, select Verify to make sure your custom domain is properly registered and is valid.

Common verification issues

If you can’t verify a custom domain name, try the following suggestions:

1. Wait at least an hour and try again. DNS records must propagate before you can verify the domain. This process can take an hour or more.
2. Make sure the DNS record is correct. Go back to the domain name registrar site. Make sure the entry is there, and that it matches the DNS entry information provided in the Microsoft Entra admin center.
   1. If you can’t update the record on the registrar site, share the entry with someone who has permissions to add the entry and verify it’s correct.
3. Make sure the domain name isn’t already in use in another directory. A domain name can only be verified in one directory. If your domain name is currently verified in another directory, it can’t also be verified in the new directory. To fix this duplication problem, you must delete the domain name from the old directory. For more information about deleting domain names, see Manage custom domain names.
4. Make sure you don’t have any unmanaged Power BI tenants. If your users have activated Power BI through self-service sign-up and created an unmanaged tenant for your organization, you must take over management as an internal or external admin, using PowerShell. For more information, see Take over an unmanaged directory.

Credit : https://learn.microsoft.com/en-us/