Every house and every flat has its own letter box — or “inbox” in geek slang — which gets filled (almost) daily by the postman. So the letter box acts as a container for incoming stuff.

But what is with outgoing stuff? We have to bring it to the next post box or post office. Wouldn’t it be much easier to use the letter box also for outgoing mail? When the postman brings the mail, he could also pick up the outgoing mail.