My wife is a treasurer for an organization, and all of their expenditure receipts must come to her. Quite regularly, an envelope without a stamp drops through our mail slot with the latest batch of receipts. The man who delivers these letters to us is a federal criminal, but I doubt he knows it. It's possible that the law he is breaking turns more of us into federal fugitives from justice than any other. We're a nation of criminals.
In order to assure a reasonable income for the US Post Office, our government grants them a monopoly to deliver mail. One of the things that makes messenger services so expensive, is that they must actually pay the USPO the going rate for most of their own deliveries. Remarkably, that monopoly extends to your mailbox, and to the hole in your home that one is expected to push mail through. I confess to breaking this law many times when our kids were young, when there were party invitations to deliver. Have YOU broken this law?