Who Can use my Mailbox or door mail slot?

The law that you are looking for is called "The Private Express Statute". What was done was a violation of the law and among local ordinances its also considered littering and is punishable by a fine. Call the business listed on the flyer and ask them who does their small time advertising. You Can then file a complaint with the local police because its highly unlikely that the Postal Inspectors will get involved because there is not enough bang for their buck.

I'm not sure about a door slot, but if it was placed in a mailbox of any kind, it is against the law. Check with the post office, they will know.

And get rid of the mail slot - that is a big security risk for you and your family. It makes breaking into your house much easier.

Try contacting the Post Office and ask if there is a mailbox or a postal outlet in your area you can drop your mail off.

Your mail carrier can tell you the answer. But if you don't know who put it in your mail slot, who will you blame? Be grateful you did not receive the collections of someone's pooper scooper in your mail slot.