MSExchangeTeam blogged about RBAC which is the new permission model introduced in Exchange Server 2010.
Role Based Access Control (RBAC) is the new permissions model in Microsoft Exchange Server 2010. With RBAC, you don't need to modify and manage access control lists (ACLs), which was done in Exchange Server 2007 and earlier. On the flip side - as with anything new, RBAC can seem a bit intimidating at first.
I am going to try an explain how to think about RBAC, and the order to create things in so that you end up with a working RBAC setup that does exactly what you want. As we go thru each piece we will be setting up a custom role so feel free to follow along with the commands in your environment.
Read more at source: http://msexchangeteam.com/archive/2009/11/16/453222.aspx