external remote locking postbox that can be accessed by Amazon and the household.

I have seen several reports that Amazing sell a door lock, presumably for the savvy to fit on their porch door. But I can see people fitting it to their front door. Or your mega post box DtG. Put a big sign on it for Bill the Burglar to read (in words of one syllable).

I would guess it has to be within range of the WiFi, and its battery "in charge". Can't see any hardware on sale there but maybe this is just vaporware. Like the drone deliveries. But it will happen, you can bet on it.

And yes, how does it affect your insurance? I would bet the car is immobalised for the duration so that Sam the Sneaktheif can only take from the contents of the vehicle. And the delivery driver is a witness.