Source : Free On-Line Dictionary of Computing

mail exploder
     
         Part of an {electronic mail} delivery system which
        allows a message to be delivered to a list of addresses.  Mail
        exploders are used to implement {mailing list}s.  Users send
        messages to a single address and the mail exploder takes care
        of delivery to the individual {mailboxes} in the list.
     
        (1996-02-26)