Under the Azure Active Directory | Custom domain section, click Add custom domain and complete the verification process to prove that you are the owner of the domain:
Actual configured domains
Add the TXT entry shown to your DNS zone to verify the domain:
Domain verification options
Click the Verify button on your Azure portal, and after successful verification, the new DOMAIN NAME will appear under DOMAINS. Choose the Make primary option:
Custom domain overview and configuration options (Make primary or Download the Azure AD Connect tool)
Open https://portal.office.com to complete the domain setup process under the admin section:
Office 365 setup wizard
Choose the custom domain to be used for email addresses:
Sign-in and mail options
The last step we need to take is to set the new UserPrincipalNames to the existing users. We do...
