Come on my property without a warrant or an invitation and I don’t care what uniform you’re wearing. UPS and FedEx drivers excepted.
I would argue that when you order a product (or otherwise agree to have something shipped or mailed to you) you have de facto given permission (unless instructed otherwise) for the mailman, UPS driver or Fedex driver to enter your property for the *sole* purpose of dropping off your package, getting your signature (if necessary) and then leaving.
Thus, an invitation is implied in that case.