According to the United States Postal Inspection Service, mail tampering is any obstruction that potentially prevents the legal pick up and delivery of mail by a postal worker. This includes damage to or destruction of a mailbox, delivering mail or other items to a mailbox through any means other than the postal service, mail fraud, mail theft or submitting a false change of address to the postal service.
The Legal Information Institute at Cornell University Law School notes that anyone who knowingly or willingly obstructs the passage of mail through the postal service could face a fine or imprisonment for up to six months. Destruction of a mailbox or of the mail within a mailbox can result in up to three years in prison.
Residential-Mailboxes.net notes that all mailboxes, including residential mailboxes, are property of the postal service no matter whose property the mailbox sits on or who paid for the box. Homeowners and others cannot hang anything on a mailbox, remove it, destroy it or relocate it without it being considered mail tampering and a federal crime. Removal of mail by anyone other than the homeowner or authorized agents can also be considered mail tampering. No one other than a postal service employee is legally allowed to deliver items to a mailbox.