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.