Physical mail, at least in the US, enjoys privacy due to specific law. As I understand, a court order/warrant is needed to open a USPS letter.
With private carriers like FedEx (which aren't allowed to offer normal letter service in the US) there's no such restrictions. FedEx directly states "We may, at our sole discretion, open and inspect any shipment without notice."[1]
With private carriers like FedEx (which aren't allowed to offer normal letter service in the US) there's no such restrictions. FedEx directly states "We may, at our sole discretion, open and inspect any shipment without notice."[1]
1: http://www.fedex.com/us/service-guide/terms/express-ground/i...