Someone else can confirm but they may have stopped allowing mailed packages. I know they no longer allow 3rd party drop offs which is why Dreams Unlimit now mails their gifts.
Your best bet would be to check with your pre-cruise hotel to see if they will accept a package for you, and then see if they'll slap a luggage tag on it at the port.
Not sure about any new rules, but as recent as last year I have shipped a package to the boat and it was delivered safe and sound to my room. I've done it twice, and both times I had no problems whatsoever.
We are on the bus heading back to the airport just off the Dream. We had a box of surprises shipped to us and it was there.
We went to guest services on deck 3. Inquired about how to get a package that was mailed to us. When we got back to our stateroom after dinner, it was in our room !
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