In the olden days, before Amazon Prime, people still had daily deliveries to their homes. In the United States, this often consisted of a daily drop off of fresh milk. The milk could be left at one's front door. But to hide bottles from casual thievery and make the milk easier to grab while still inside the house, some homes had milk doors. These were cabinets built into the outside wallk, accessible through doors on each side.
They weren't locked, but, as Rain Noe of Core77 points out, they represent a similar approach to the delivery lockers that some people use to prevent "porch pirates" from making off with their property.
Perhaps, in the future, homes will have built-in delivery lockers to support this new instant delivery lifestyle.
Photo: Downtowngal