It probably works like the multi-customer mailbox that we installed in a commercial building a couple of years back. The mail box comes with holes drilled for a post office provided lock as well as a fully installed lock and key for the customer. You install the mailbox and then call the post office and they send someone out to install one of their locks in the pre-drilled hole. I am not sure if they charge for that or not. That was above my pay grade. I would imagine that they do.Impressive mailbox, I didn't read about it, but I am curious, do you know how the mail person can open it, but no one else can?
Here is a photo of the model mailbox we installed. As you can see each tenant has a key for their individual mailbox, but the keyhole above the label is for the lock that the post office installs, and for which only they have a key. It allows the mail carrier access to all the individual boxes. (the entire front of the box tilts out exposing the open tops of each mailbox).