Yeah, it's a goofed up law and it takes a lot of careful reading of the statutes - a few of us bros hashed this out on the boards 1-2 yrs ago and now everyone seems to agree - most everything you can do (export import buy sell bla bla etc.) is illegal, but possession is not.
Every time you go to the mailbox to pick it up you could still be busted, so it's not like there is no risk. But once you have your stuff inside the house, unpacked, and tucked away, you can rest easy.
This does not apply to recreational drugs (cannabis, cocaine, etc.), needless to say, ... possession of these is definitely illegal!