At least around here (in US), while street deals are still the common among most people, USPS is likely the one of the biggest/safest methods now. They require

At least around here (in US), while street deals are still the common among most people, USPS is likely the one of the biggest/safest methods now. They require a warrant to search domestic packages, not to mention the most common "illicit substance" is now commercially legal in many states...