Is it mandatory to have your own domain to use a Microsoft 365 tenant?
The straightforward answer is ‘No’. A Microsoft 365 organization can function without its own domain. This section explains how a Microsoft 365 tenant operates without your own custom domains. It’s also important to understand the concepts listed here, as the individual domains added to the Microsoft 365 environment are considered accepted domains in Exchange Online.
Does Microsoft 365 include domains?
Yes, when you register for Microsoft 365, your organization is assigned a default domain like ‘company.onmicrosoft.com’. This domain is used by default for email addresses or aliases unless you add a custom domain and set it as the default for your Microsoft 365 setup.
You can also add another onmicrosoft.com domain if needed. A common reason for adding additional onmicrosoft.com domains is to perform a SharePoint domain rename to match the organization’s rebranding. Once an onmicrosoft.com domain is added, it cannot be removed from the Microsoft 365 environment.
What is fallback domain in Microsoft 365?
By default, the onmicrosoft.com domain provided when creating the Microsoft 365 tenant will be the fallback domain. However, you can change the fallback domain by adding another onmicrosoft.com domain later.
A fallback domain in Microsoft 365 is used as a backup when the primary domain cannot be used for certain operations or configurations. A fallback domain is particularly useful when the primary domain is unavailable, ensuring that your users' emails are still routed successfully.
How many domains can be added to the Office 365 tenant?
You can add up to 5,000 domains to a Microsoft 365 subscription, including both custom domains and a maximum of 5 onmicrosoft.com domains.