Pre-Exchange 2010 vs. Exchange 2010 Permission Models

Microsoft Exchange Server 2010 now comes with the new RBAC (Role Based Access Control) permissions model. This new permissions model allows you to define both a broad, as well as a more granular assignment of permissions to administrators. The roles you assign to administrators can reflect more accurately the actual roles they perform in your organization.

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http://www.petri.co.il/rbac-in-exchange-2010.htm