I suggest you read the postal regulations. It is illegal to put fliers in or on any mailbox in the USA.
Advertising on a mailbox or its supporting post is prohibited.
Our regulations cover what can and canít be placed in a curbside mailbox or mailbox outside of your house, which generally includes only mail that has been sent through the USPS. However, our regulations donít govern what can be placed in a mail slot on your door.