Yes, in the United States, it is illegal to place anything inside a mailbox that has not been processed through the United States Postal Service (USPS). This regulation is established under Title 18, Section 1725 of the United States Code, which prohibits the placement of mailable and non-mailable items alike in mailboxes without proper postage. The law is intended to protect the security and integrity of the postal system, ensure the privacy of mailbox owners, and preserve the revenue of the USPS.

Violating this law by placing flyers, brochures, packages, or any other items directly into mailboxes without going through the USPS can result in fines for each offense. The USPS is very clear about this regulation, emphasizing that mailboxes are intended solely for the receipt of postage-paid mail.

Businesses or individuals looking to distribute advertisements or other materials have legal alternatives, such as…

• Using door hangers placed on doorknobs.
• Hand-delivering items directly to the recipient without using the mailbox.
• Mailing items through the USPS with appropriate postage.

These methods ensure compliance with the law while still allowing for the distribution of marketing materials, messages, or packages.