Adding a UPN suffix to your domain

If your AD domain doesn't match the DNS domain you want to use in Office 365, or if you have multiple DNS domains you want to use for login names, you'll need to add additional domain suffixes to AD.

Doing so is quite easy. In your domain controller, go to Active Directory Domains and Trusts, right-click the very top node as shown, and choose Properties. From there, add the suffixes you want to support:

AD additional UPN suffixes

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