A big problem for people on vacation is having to get their mail collected. A big pile of mail in the box strongly suggests that the house is vacant, and thus ripe picking for theft. The usual solution is to have a friend pick up your mail.
But let's say your friends are all busy. Now what?
Okay, let's build, inside the mailbox, a trap door, which leads a ramp, that slides the mail down to a small container in the basement. (Or, for slab houses, under the house. A chain lifts this container up to the main house, where it empties onto a desk.) The trap door is triggered by a certain weight in the box, so mail never builds up past a certain point.
Also, if I make the weight threshold low enough, no one can ever steal your mail again. Even if you are home.