considering the fact that every year over two hundred billion pieces of mail are sent via USPS, it really is impossible for them to do very intensive screening on the mail. Fuck cocaine residue being on 95% of money, a lot of the sophisticated mail scanning technology that LE has takes several minutes to run on a single parcel. It is just impossible for them to keep delivering mail at the required rate if they subject more than a small % of it to those sorts of technologies.