If you don’t already have your own domain, you can easily buy one online, for example from a domain registrar or a domain reseller. You get a domain name when you sign up for Office 365, for example, contoso.onmicrosoft.com. But you may want to use a custom domain name, like fourthcoffee.com.
To set up a domain in Office 365, you must own a domain and change some of the DNS records for your domain.
Caution Some domain registrars or DNS hosting providers don’t allow creating all the DNS records required by Office 365. Hosting providers in the following list support all the needed records. If you’re thinking of using a different hosting provider, learn about potential service limitations.
You can use your own domain with Office 365 to personalize your email addresses, instant messaging addresses, and your public website on Office 365. After you register your domain (at a domain registrar), you sign in to Office 365 as an admin and set up your domain so you can use it with your email address and other services.
Domain registrars that support all DNS records required for Office 365
Tip Using the Office 365 Enterprise subscription? You can buy a Go Daddy domain directly from the Office 365 portal. On the Admin page, click Domains, then click Buy a domain.
Transfer your domain to a different domain name registrar
If your domain is registered at a provider that doesn’t support all the necessary DNS records, you can transfer it to a different provider. When you transfer the domain, you change who you send payments to in order to renew and keep your domain name.
Request the transfer at the registrar that you want to move your domain to. Look on their website for an option such as Transfer DNS. After they make the changes, it can take a few days update across the internet.