What is the DNS domain name of my Active Directory?

When you register your Directory Update software, the software is licensed we need to know your Active Directory DNS domain name for the domain in which Directory Update will be used. The software is licensed to that particular Active Directory domain name.  Please note that this domain name might not be the same as your Internet domain name.

The best way to figure this out is to launch Active Directory Users and Computers. The domain name is the one shown at the top of your domain tree. It is circled in the picture below.