Mail bomb

A mail bomb is a form of denial of service attack. The idea is to flood someone's system with more e-mail than it can cope with.
There are two ways to make a mail bomb. The first is to send millions of e-mails to one address simultaneously. This leads to the system filling up and crashing. The second is to send small compressed files that, when decompressed, expand to extremely large files, again filling up the e-mail server and causing a crash. One example of this is the Win32.Netsky.J worm.