In my previous article I thought about using the letter boxes also for outgoing mail.

An additional function of a letter box could be to act as a container for waste paper. So we would have a nice cycle: the postman first brings the mail, and later he picks up what ended as waste paper (which then can be recycled). And the people no longer have to store the waste paper for the next waste paper collection or to bring it to the collecting point for waste paper.