OUTLOOK EXPRESS BACKUP FILE

Question

My Toshiba Satellite with MS Vista appears to make backups of my email files (folders) according to some pre-scheduled setup instructions (transparent to me). These files showup in the Recycle Bin bearing a .BK extension. I've been unable to restore them however. For some unknown reason, some of these email file folders just vanished a few weeks ago. I thought "no particular problem". I'll just restore them with these backups but I'm not able to. Am I wrong about this - it's not possible to restore them? Or, these folders with the .BK extension aren't backups like I thought??. .