The link has changed in 2013, here is the new location of my article :
http://blogs.technet.com/b/mspfe/archive/2010/11/23/securing_2d00_ms_2d00_exchange_2d00_2010_2d00_role_2d00_based_2d00_access_2d00_control_2d00_rbac_2d00_simplified.aspx
Sam