Use a vanity domain for your SharePoint Online public website address
When you host your company website on Microsoft SharePoint Online, as an administrator, you can choose to change the site to use a vanity domain name instead of continuing to use the domain you chose when you signed up for Microsoft Office 365 for professionals and small businesses: for example, contoso.sharepoint.com. Changing the domain name for your public site enables customers to access your site by using an existing domain name that you own, or a new domain name that you’ve chosen and purchased for your business.
To use your vanity domain with Office 365, you first add your company’s registered domain name to the service. For more information, see Add and verify a domain. After you’ve added your domain, you can configure Office 365 to use the domain name for your public Office 365 website. For more information about setting up a website on SharePoint Online, see Set up a public Website.
You can host one website with your Office 365 account, and you can point only one domain to the website. Also be aware that you cannot use Secure Sockets Layer (SSL) protocol with an Office 365 hosted site.
After you configure Office 365 to use your vanity domain for your website, you can easily change the site to use another vanity domain name or change back to the original domain name that you used (for example, contoso.sharepoint.com), by following the steps provided in this topic. Or you can, if you like, choose at a later time to move the site to be hosted by another third-party service.
To configure Office 365 to use a vanity domain for your public website, follow these steps.
On the Admin page, in the left pane, under Management, click Domains.
Click Change address, and then step through the wizard.