You go into Active Directory, choose the user you want to hide, double click to get the properties, click the Exchange Advanced Tab and select ... Hide from Exchange address list.
Or .. in System Manager - Click Help - type 'hide' and the 4th one will tell you exactly the same.
Marc
If 'something' 'somewhere' gives 'some' error, expect random guesses or no replies at all. Please specify details.
Free Tip: The F1 Key does NOT destroy your PC!