The Jargon File (version 4.4.7, 29 Dec 2003):

mailbomb


    (also mail bomb) [Usenet]

    1. v. To send, or urge others to send, massive amounts of email to a
    single system or person, esp. with intent to crash or spam the
    recipient's system. Sometimes done in retaliation for a perceived serious
    offense. Mailbombing is itself widely regarded as a serious offense ? it
    can disrupt email traffic or other facilities for innocent users on the
    victim's system, and in extreme cases, even at upstream sites.

    2. n. An automatic procedure with a similar effect.

    3. n. The mail sent. Compare letterbomb, nastygram, BLOB (sense 2), 
    list-bomb.