W2K Excnge- Edit syst message Size Limit

I want to edit the message that the system sends a user when his mailbox size gets too large. In user properties under active directory you can limit the isze of a users mailbox. When the box gets to that size the system automatically sends him a message “Your mailbox is too large it has exceeded……..” In the message it tells users to move stuff to their .pst file which I don’t want them to do. EXACTLY how can I edit the text of the system message>