Letter: Post Master discusses customer mail receptacles
Use for Mail
Mail receptacles may be used only for matter bearing proper postage.
No part of a mail receptacle may be used to deliver any matter not bearing postage, including items or matter placed upon, supported by, attached to, hung from, or inserted into a mail receptacle. Any mailable matter not bearing postage and found as described above is subject to the same postage as would be paid if it were carried by mail.
Customers must keep the approach to their mailboxes clear of obstructions, these include, but are not limited to, snow, vehicles, motorcycles, animals, bicycles, trash cans and so on, to allow safe access for delivery. If USPS employees are impeded in reaching a mail receptacle, the postmaster may withdraw delivery service.
Any advertising on a mailbox or its support is prohibited.