When configuring per-server segmentation, the settings are applied for all user’s with mailboxes hosted on the Exchange server.  To enable segmentation per-server,

1. Open the registry editor (Start\Run\Regedit)
2. Locate the following registry subkey: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeWeb\OWA.
3. Create a new DWORD.
4. In the New Value #1 box, type DefaultMailboxFolderSet.
5. Right-click and select Modify.
6. Select Decimal and type the value that corresponds to the OWA features to be enabled.  Refer to Microsoft article http://support.microsoft.com/kb/833340 to calculate the segmentation value.
7. Click OK to apply the changes.

Note: In a front-end / back-end environment, segmentation settings must be made on the back-end server.  

For additional information about the segmentation attributes, refer to Microsoft’s article below.http://support.microsoft.com/kb/833340.