Mailman puts the package in the mailbox which has a keypad and low-tech 1980's calculator style 1 line display.
He put package in locker. It generates and displays a pin-code, he write it down on a slip of paper with the locker number and puts it in your mailbox.
Works very well.
(I think he has to swipe a card to allow him to lock the thing in the first place. To stop random people using it).