Mailbox use is tightly regulated by the US Postal Service, which is not a surprise, but while I was researching whether or not it is legal for non-postage items to be pushed through our garage mail slot (it appears it is), I noted that they do give a tiny bit of leeway: “Generally, curbside mailboxes are to be used for mail only. However, publishers of newspapers regularly mailed as Periodicals may, on Sundays and national holidays only, place copies of the Sunday or holiday issues in the rural route and highway contract route boxes of subscribers if those copies are removed from the boxes before the next scheduled day of mail delivery.” How considerate of them. (from DO41 PDF file)