Hide email adress of sender when sending on behalf of
Solution 1:
Outlook supports different identities. Take a look at this description: http://support.microsoft.com/kb/829918/en-us
Solution 2:
I managed to solve the same problem. I just removed the permission to "Send on behalf" on the ESM - Exchange 2003 (the target sender was a public folder). Then on the public folder "directory rights" I added the sending user with the "Send As" permision. Worked quite well!
Hope it helps!