Source : Free On-Line Dictionary of Computing

mail bomb
     
         To send, or urge others to send, massive amounts
        of {electronic mail} to a single system or person, with intent
        to crash or {spam} the recipient's system.  A successful mail
        bomb may cause the victim's {disk quota} to be exhausted, the
        disk holding his mailbox to fill up, or his computer to spend
        a large proportion of its time processing mail.
     
        Mail-bombing is sometimes done in retaliation against someone
        persistently abusing {Usenet} and violating {netiquette}.
        While it may inconvenience the intended victim (if they gave
        their real address), it will probably also inconvenience other
        users and administrators of the computers and networks
        involved.  Mailbombing is thus a serious offense itself.
     
        See {netiquette} for the correct way to respond to perceived
        violations.
     
        Compare {letterbomb}, {nastygram}.
     
        [{Jargon File}]
     
        (1995-04-04)