To better assist you on this, what Azure service are you leveraging? What is the specific requirement that you are attempting to accomplish?
Kindly see these docs:
Quickstart: How to send an email using Azure Communication Service - In this quick start, you'll learn about how to send email using our Email SDKs.
Quickstart: How to create authentication credentials for sending emails using SMTP - In this quick start, you learn about how to use an Entra application to create the authentication credentials for using SMTP to send an email using Azure Communication Services (ACS).
Also, see: Map an existing custom DNS name to Azure App Service -To migrate a live site and its DNS domain name to App Service with no downtime, see Migrate an active DNS name to Azure.
Kindly let us know, I'll follow-up with you further.