http://support.microsoft.com/kb/824126
The Exchange Information Store automatically redirects all restore operations to the Recovery Storage Group (if a Recovery Storage Group exists on the server). When a Recovery Storage Group is created on a server, Exchange checks to see if the database that is selected for the restore operation is present in the Recovery Storage Group. If it is present, the database files are restored to the Recovery Storage Group. If it is not present, the restore operation stops.
Hope this helps.