USPS Informed Delivery is a free service offered by the United States Postal Service that allows users to preview their incoming mail. Subscribers receive daily emails with images of the front of their letter-sized mailpieces, helping them stay informed about what to expect in their mailbox. Informed Delivery also provides notifications for packages, allowing users to track their shipments. This service can be accessed through the USPS website or mobile app, making it convenient for users to manage their mail and packages from anywhere.