@GHC, how are you setup? If you are deleting email on your BB and it automatically deletes from your Outlook, then it sounds like you are on BES already.
@Dubdub, you are correct, if he disabled his BIS during the day (what a pain!) when he re-enabled each day he would get all the mail anyway. It's just as easy to hit delete on the BB, or hold down the NUM key and scroll to select a large group of emails on the BB to delete all at once, takes 5 seconds to delete a screen full of emails.