Apple Mail configured to use exchange but To and CC addresses coming from other sources How can I limit the recipients to just contacts from the Exchange directory? When I start typing in the "to" field, not only are my options people in my exchange directory, but also people in my GMail contacts list!  I only want people from my exchange directory to show up in To, CC and BCC.
The solution is to go to Window-> Previous Recipients and remove those you don't want.  This is discussed in the help page "Manage email addresses in the Previous Recipients list".