Crimes involving the mail occur at the federal level because the U.S. Postal Service is part of the U.S. government. Therefore, the mail falls under federal jurisdiction. This does not mean that local officials can not be a part of investigations or arrests concerning mail crimes, but it does mean that if you face a charge for mail fraud, you will do so in a federal court under federal law.
According to the U.S. Department of Justice, mail fraud is a simple crime. There are only two elements that incorporate this crime. You must use the mail to commit fraud. The elements are using the mail and committing fraud. Both of the elements must be present in your case to prove mail fraud.
Any type of scheme or scam intended to commit a criminal act of any type is mail fraud. This could include something as simple as sending a letter to someone and requesting money for a fake debt, or it could be a complex scheme involving many people who send out mailers promising something in exchange for money. The victims often will lose money but could also suffer other damages.
This is usually not a violent crime, but that does not mean it does not cause harm to victims. Victims of mail fraud may lose a lot of money, which could then lead to financial troubles. Some victims may end up losing their homes through foreclosure or financing frauds perpetrated through the mail. Victims could suffer stress due to some scams, and this could lead to health problems.