For some reason when you use the Public Folders tool in Exchange 2007 SP1 you can’t change the client permissions for the public folders. So to do so, follow the below steps:
1) Logon to your ‘Exchange 2007’ server.
2) Open the ‘Exchange Management Shell’.
3) Type the below, replaceing ‘public folder name’ with your public folder name/path and you must keep the \ at the front of it and also replace ‘username’ with the username:
Add-PublicFolderClientPermission -Identity "\public folder name" -AccessRights Owner -User username
That’s it, just repeat for any other public folders that you wish to change the permissions on.
The above example is to assign Owner permissions to the user, but you can replace Owner with the below: