Use a custom domain name for your SharePoint Online public website address
When you create a public website on SharePoint Online, as an administrator, you can set up the site to use a custom domain name instead of using the domain name that you chose when you signed up for Microsoft Office 365 for enterprises, for example, contoso.sharepoint.com. This helps customers find your website by using the more familiar domain name that you bought for your business.
To use a custom domain name with Office 365, do the following.
If you haven’t already done so, add your company’s registered domain name to Office 365. For more information, see Add your domain to Office 365.
Note
When you add your domain name, you must specify the services in Office 365 with which you intend to use it. When you’re asked, choose SharePoint Online. For more information, see Specify the services you’ll use with your domain.
Set up SharePoint Online to use the domain name for your public-facing Office 365 website.
When you create a new site collection in SharePoint Online, you see a drop-down list that shows the domain names that you can use for the site. The domain name that you added to Office 365 is in the list. For more information, see Set up a public website.
The steps here help make sure users can see your website when they type, for example, www.contoso.com. If you also want them to see your site when they type just the domain, contoso.com, contact your DNS service provider and ask if they have a URL redirection service to direct traffic from contoso.com to www.contoso.com. Most providers offer URL redirection, and you can check their documentation to learn how to set it up.