In Exchange 2007:
Open EMC
Expand Org Config
Expand Hub Transport
Right-Click "Default" under Remote Domains
on the tab that reads "format of original message..."
Check or Uncheck "Allow automatic forward"
In Exchange 2003:
User Exchange System manager
Expand Global settings
Select Internet Message Formats
Right click "Default" under internet message formats
Select the advanced tab
Check or uncheck "Allow automatic forward"
Here is a link:
http://www.howto-outlook.com/howto/automaticreply.htm