On one hand, the pool of likely suspects is rather small, and the punishment can actually be rather big if it's USPS, since it's a federal crime. I see that mail fraud laws apply to other carriers such as UPS/Fedex, but I'm not sure if that also extends to mail theft. That said, the reason it applies is because they cross state lines, so I'm not sure if the specific case has to include that as well, which if we're talking about drone delivery, is unlikely.