I would like to host 1 domain name, but I want to keep most "customers" separate from seeing each other (private from the whole). It other words, I may have a small group of individuals who should remain grouped with the ability to see & share exchange resources, but I will also have a few that should be totally isolated from the rest. Remember, they'll all have the same domain name. Is this possible WITHOUT the Exchange 2010 hosting mode? Or, does this have to be done with Exchange 2010 hosted mode?