Within many jurisdictions, mail tampering is a crime and is punishable by incarceration, fines, or a term of probation. Within the United States, mail tampering is often a crime under state laws; however, mail fraud is a federal crime. The definition of mail tampering will vary by jurisdiction, but generally includes opening, destroying, damaging, or interfering with mail intended for another person.

Under most states laws within the United States, mail is considered private property. As private property, an individual has an expectation of privacy attached to his or her mail. When another person breaches that expectation of privacy, he or she may be guilty of mail tampering.

State laws differ; however, in most cases, no one is allowed to open mail intended for another person. In many cases, even members of the same household cannot open mail addressed to another member of the household. State statutes do frequently make an exception for United States Postal workers or other carriers if they are acting in good faith when opening the mail as part of their job.

Destroying, damaging, or interfering with the mail are also often considered mail tampering. For instance, removing mail from someone's mailbox or throwing mail away that is intended for another person may amount to a crime. Under most state statutes, mail tampering is a misdemeanor and is punishable by a term of imprisonment of up to a year or two.

Mail fraud is another crime that involves the mail; however, unlike mail tampering, mail fraud is a federal crime. Mail fraud involves using the United States mail to carry out a scheme or plan to unlawfully obtain money or anything else of value. Mail fraud is often used as a reason to make what would otherwise be just a violation of state law a federal offense.

Mail fraud may include elaborate schemes to steal money from victims by convincing them to send money to a non-existent charity, for example. The connection to the U.S. Postal Service may not be as obvious, however, in other cases. Basically, if even one check, document, or package was sent through the U.S. Mail during the course of a crime, then mail fraud may be charged elevating the crime to a federal crime. In reality, many crimes could be charged at the federal level using the mail fraud charge; however, in reality, federal district attorneys are selective regarding when they choose to file charges of mail fraud in order to elevate a state crime to the federal level.