We don't have envelopes that have 2^256 possible keys with only one that opens them. We cannot protect from dogs hitting on packages, I suppose this would be a fingerprinting attack. We cannot protect from tracking devices being placed in packages. We cannot get around customs if it is legit. Pretty much nothing we could do would come close to as effective as USPS, and anything we did would be just as vulnerable anyway. However, It would be possible to do this with dead drops in a city wide area for small orders, with bigger traffickers driving bulk product from place to place. The primary thing that prevents this from happening is that we have not reached critical mass yet. If there were maybr 50X as many people involved it would be more feasible. Then vendors would start to supply only the people in their city, and product transfer would be done via dead drop and similar. If they ever get a lock on the mail system we will have to resort to this, but right now it just isn't worth it for vendors. Vendors can use mail to reach customers around the world, giving them a much larger customer base. With the exception of major cities, a lot of vendors here probably don't live in geographic proximity to more than a few dozen SR customers, and those customers may not be interested in the products the vendor sells. If every city on earth had 50X as many SR members, it would be a lot more feasible for vendors to stop doing international and national vending and start to focus on city wide vending, and in such a case we would no longer need to use third party delivery systems at all.