By default, only users on your Google Workspace domain or Microsoft tenant can access AODocs on your domain.
As an AODocs super administrator, you can extend access to external users or domains using allowlists. Learn more:
A Google domain can manage different domain names (primary, secondary and alias domains). The primary and secondary are, by definition, different. Users from the same Google domain can be user1@primaryDomain.com and user2@secondaryDomain.com. Even with different domain names, they will both be internal users of the Google domain primaryDomain.com.