(1) and (2) do not really apply to letters (i.e., communication), (3) only applies when crossing borders, and then it's not the postal/delivery service that is

(1) and (2) do not really apply to letters (i.e., communication), (3) only applies when crossing borders, and then it's not the postal/delivery service that is opening the package, but customs, and (4) at least over here would be illegal, too, if it can be used to read the mail. Both opening/reading the mail that you are supposed to deliver as well as listening to phone calls going through your network is a criminal offence.