This may not be what you want to hear, but may help you and your recipient really getting what you are sending:
Do NOT send it by mail.
Even if you send it for pickup at the mail office, it is not likely to get there in a useful time frame. And if it does, who ever picks it up, may be surprised that all there's left in it (if it was in any valuable) may be little more than packaging material. I have seen it and more than once (that's more than twice too).
Have your friend check in with the Vimenca office in Cabarete or Sosua and ask them to open
Miami shipping account with them.
In Sosua, there also is BankerTrust (they advertise on here on dr1) which offer a similar service. You will then receive an address and shipping routing code to a Miami forwarder and about 2 working days later, your addressee here in Cabarete, Sousua, Puerto Plata can retrieve your package for about USD $3.oo to $4.oo per Lb.
That's easy, cheap if not cheaper, fast and has a 99.9% likeliness to go into the books as a successful transaction.
Good luck! ... J-D.