Your mailbox is out of limits. You don’t even own it. The moment you put your mailbox in front of your house, you abide by the rules of the post office. And if you use it for anything other than the postal business (and pay the fees), you’re looking for a battle.
Below is a direct quote from the USPS Postal Gazette (Issue 21861, 2-17-94, p. 37):
Mailable Material in or on Private Mail Receptacles Unsealable mailable material in or on private mail receptacles represents a revenue deficiency for the Postal Service and is a violation of federal law. Title 18 of the United States Code, section 1725, establishes a fine of not more than $300 per piece for these violations. All employees must uniformly enforce the procedures detailed in the Domestic Mail Manual, section P011.2.0. The lack of uniform application of these procedures may jeopardize the criminal prosecution of repeat offenders.
This is not intended for the accidental piece of mail that was dropped in the mail stream without a stamp. Although we spend $20 to $30 to buy and install a mailbox in front of our house, that mailbox is designed, even by law, for the exclusive use of the post office.
If the local pizza delivery joint walks through your neighborhood, they may not place their ads in your mailbox. They can’t hang it from a string, they can’t stick it inside, and they’re not allowed to stick it in that little space between the red flag and their box. Not allowed. The same goes for the paper delivery guys. They can hang their stuff on your door, stick it through the crack in the door, drop it into your milk crate, and if they’re feeling really brave, even give it to you. But they may not deliver it to your mailbox without paying the appropriate postage. If you find this “non-mail” invading your mailbox, and it really bothers you, call your local postal inspector. They will stop him very quickly. Technically, your neighbor can’t even leave a message in your mailbox unless he also pays for the postage.
I’m not particularly in favor of the stringency of this law, but its existence has allowed the USPS to maintain its monopoly on mail flow, which means that, overall, our postal service has the highest volume of any country, and thanks to scale economics. and with no serious competition, we also have a reasonable first class and wholesale postage rate (even at .42 for first class (or the new .44 rate that goes into effect mid-May, still lower than most in any other place).
Why the Post Office Needs a Postal Monopoly: If the USPS delivered only 3/4 of today’s mail volume, they would still have to keep nearly all of their existing Post Offices and employees on the payroll open, and would have to make up the difference with a much higher postage rate. Otherwise, they would have to reduce the service, and nobody would like that. Therefore, this decision, which prevents mail from not reaching mailboxes, actually works in our favor.