New Registered Domain in Domino Environment

Currently we have one mail server housing three different companies. They are all kind of under the same umbrella however three different entities I guess you can say. We want to now branch out and give each of the three companies their own respective domino servers with their own domain. How can this be done within Domino?

Example : Currently we have MailServer/Domain1. We would now like to have MailServer/Domain2 & MailServer/Domain3. How do you create a new server with a new domain, which we do have registered? Can you do it from the Admin client that is being used for the current Domino Domain?

Thanks ahead of time for any direction.