At-home mail pick up

Simple idea but not universally implemented makes you wonder why. Every letter box should have 2 slots designated as in and out. The postman delivers mail into the in-slot and takes mail from the out-slot. If you expect mail, you don't have to go to the post-office or the nearest drop box to post your mail. The postman will head back to the post-office anyway so why not take your mail. It saves time and costs nothing. Why doesn't it become universal practice?

http://www.thinkaloo.com