Mastering Office 365 Administration

DNS domains

While DNS domains aren't exactly like users and groups, they haven't been covered elsewhere. Without a custom DNS domain, all your users will end in @tenantname.onmicrosoft.com. Since domains have a direct impact on the user names you can provision, we'll review here what it takes to add a domain to Office 365 and configure it so that you can use it as the suffix for login names and email addresses.

An important caveat: domain names in Office 365 are first come, first served and must be unique across the entirety of all Office 365 tenants worldwide. Therefore, if you added a domain to an old trial account or some other department in your company is also working within Office 365 and added the domain to their tenant, it will not ...