Adding a custom domain to Office 365 is a key step in the deployment process. Microsoft added the Domain Quickstart Wizard to the service to assist you through the process. The key feature of DNS for Plan P1 is that Microsoft hosts the DNS services for your domain. This ensures that your DNS settings are correct and remain updated as new services become available. Even so, you can continue to host DNS at your existing service provider if you need or prefer to. Many small businesses have multiple lines of business. You can add multiple domains without a problem and assign them individual users or have users with multiple email addresses. Finally, you can use the public website of SharePoint Online as your public website if you choose.