Human mail

Human mail is the transportation of a person through the postal system, usually as a stowaway. While rare, there have been some reported cases of people attempting to travel through the mail.
More common, at least in popular fiction, is the mailing of a part of a person, often a kidnap victim.
Mailing children.
The mailing of people weighing less than , i.e., children, was occasionally practiced due to a legal ambiguity when the United States first introduced domestic parcel post in 1913, but was restricted by 1914. The children were carried along by mail carriers, but were not put in boxes.