To verify your custom domain name (example)
1. Sign in to the Azure portal using a Global administrator account for the directory.
2. Select Azure Active Directory, and then select Custom domain names.
3. On the Fabrikam - Custom domain names page, select the custom domain name, Contoso.
4. On the Contoso page, select Verify to make sure your custom domain is properly registered and is valid for Azure AD. Use either the TXT or the MX record type.
Note:
There are several versions of this question in the exam. The question can have two correct answers:
1. MX
2. TXT
The question can also have other incorrect answer options, including the following:
1. SRV
2. NSEC3
Reference:
https://docs.microsoft.com/en-us/azure/dns/dns-web-sites-custom-domain