By April 14th almost every US postal code will have access to a service called Informed Delivery. The service, from the United States Postal Service, scans the outside of your mail and shows you the images each morning before the mail is physcially delivered. Subscribers will get a morning email with images of the first 10 pieces of mail, and a link to view the rest if they desire. As a security measure, USPS sends you a physical letter with a verification code when you sign up. The service is meant to be helpful to let subscribers know if an important letter is being delivered today or not.
Apparently it's a free service and you can read more about it HERE