This is the mailbox by the house I lived in when I was between the ages of 7 to 9. It is a Community Mailbox (Centralized Mail Delivery in wikipedia), from Columbia, Maryland. The idea was either that the mail carrier wouldn’t have to travel as far, so it would save money for the postal service, and/or that neighbors would meet each other at the local mailbox, and so strengthen community ties. Compared to most single-family homes in the US, where the mailbox is either at the foot of the driveway or at the front door, this is an interesting idea that has spread, but not nearly as much as Columbia’s planners might have thought they would when deploying them nearly 50 years ago. While some new communities include them (and they are standard for apartment buildings), most do not, and retrofitting existing neighborhoods is beyond the pale, no one seems to want to give up the convenience.
As mail has decreased in importance in recent years, and revenues have gotten tighter, the US post office is again pushing for these in newer subdivision. Canada is apparently going forward to putting these into existing as well as new neighborhoods.