An accepted domain is any SMTP namespace for which an Outlook Live organization sends or receives e-mail.
When do you use an accepted domain?
You can use accepted domains to enable subdomains or different domains within your existing domain.
Accepted domain functionality also makes additional domains available for additional user e-mail addresses, which are often called proxy addresses. For example, if your organization has used more than one domain for e-mail in the past, you may want to make sure that e-mail sent to a user at either domain is delivered to the user. Let's say you have a primary domain of contoso.edu and a legacy domain of contoso.net. In this case, you set up Outlook Live with the primary domain, contoso.edu and then create an accepted domain for contoso.net. When you create new users (student@contoso.edu) in the primary domain, you can also add proxy addresses (student@contoso.net) for the users. Learn more at Proxy Addresses.
You can set up accepted domains to support subdomains, which are also called tertiary domains. For example, consider an existing organization for which the first domain enrolled is contoso.edu. The administrator for contoso.edu has enrolled the domain in Outlook Live and uses the contoso.edu domain for two administrative mailboxes, postmaster@contoso.edu and administrator@contoso.edu. The primary domain is contoso.edu. The administrator then creates an accepted domain for student mailboxes only. This accepted domain is students.contoso.edu. After the administrator sets up the accepted domain, whenever the administrator creates a new mailbox, both the primary domain, contoso.edu, and the accepted domain, students.contoso.edu, are available in New Mailbox, and the administrator can choose which domain to use. In this example, the administrator would create new student accounts in the students.contoso.edu accepted domain.
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Mailboxes and Windows Live ID accounts in accepted domains are created in the same way that they are created for the primary domain. A new Windows Live ID is created with the accepted domain name that you select in New Mailbox. Your users use the new Windows Live ID, with the accepted domain, as their account to sign in.
Accepted domains don't have to be subdomains. The contoso.edu administrator can also create a new accepted domain for all alumni, such as contoso-alumni.com. These alumni mailboxes have a different domain name entirely.
As in the subdomain scenario, both the primary domain and the accepted domain are available when you create new mailboxes, and new Windows Live ID accounts are created with the accepted domain name. Also, as in the subdomain scenario, users use the new Windows Live ID, with the accepted domain, as their account to sign in.
How do you set up accepted domains?
How do you manage accepted domains?
When you set up accepted domains, the domains are added to the Outlook Live organization that you already manage. Therefore, any Windows Live ID that has administrative rights for your organization will have full access to the accepted domains that you configure.
After you set up accepted domains at Windows Live Admin Center, the accepted domains are available in the E-Mail Options section of new and existing mailboxes in the My Organization > Users & Groups > Mailboxes interface.