High Quality Content by WIKIPEDIA articles! A letter bomb, also called parcel bomb, mail bomb or post bomb, is an explosive device sent via the postal service, and designed with the intention to injure or kill the recipient when opened. They have been used in terrorist attacks such as those of the Unabomber. Some countries have agencies whose duties include the interdiction of letter bombs and the investigation of letter bombings. The letter bomb may have been in use for nearly as long as the common postal service has been in existence, as far back as 1764 (see Examples).