Aside from sending our direct invitations to new users, it's possible to use another signup mode in Luffa.
The first option is Invitation Only, the second option is to turn on acceptance of new members based on email domains. Once turned on, anyone who signs up with their domain-specific email address that matches the one you've entered will be placed in your organization. To turn on address matching signups, you can go to Settings -> Organization.
You can enter multiple domains to be accepted however, Luffa won't accept domains from free email providers such as hotmail.com or gmail.com, nor will Luffa accept domains from blacklisted sites.
Organization owners and administrations will receive an email that lists all newly registered users as well as guests who have accepted their invitation.