I've mailed cards to the DR from Canada last July and to this date the person has never received them. I've sent a book registered mail with insurance back in June/2001 and had to put an investigation on it through the postal service and the person finally received the package in October.
Last year I sent another small package, and again registered mail with insurance on it, to the address of the resort, thinking this would be better/faster. I have put three investigations on it and two weeks ago, I received a refund from Canada Post with the reason "could not trace package". The mail goes to Santo Domingo for distribution, sometimes delayed in customs, but this has got to be ridiculous. We must be thankful for our postal service.
The mail in the DR is certainly not reliable, if you done any reading on the DR, the one thing they mentioned is the not so great postal service. If you sent anything through the mail, make sure it's insured so you can get your money back. Courier services guaranteed delivery, but the cost is expensive.