Commander Tansin A. Darcos wrote:

In the United States, the postal service provides a mali reception capability for people who do not have an address. The primary use was probably for people who were transients and had no place to stay, back in the days before there were even homeless shelters. But it is still around, and how it works is you mail the item, giving the person's name, and the address of "General Delivery" stating the particular post office city and state, and (now) zip code. The recipient simply goes there with some ID to prove they are the named recipient.