Missing link? In NZ, and presumably other countries, personal letterboxes in rural areas can be used to send too, which I'm guessing is the same as what you're referring to.
Yes NZ is one of the four countries that use this style of full duplex mailbox. It hasn't caught on outside US/CA/AU/NZ, probably because (speculating here) it's not secure against theft and doubles the workload for the mailman.
Missing link? In NZ, and presumably other countries, personal letterboxes in rural areas can be used to send too, which I'm guessing is the same as what you're referring to.