Every ship has an address, and you can get this address upon your arrival at the ship at the MSA (Manning Services Administration) or Crew Services Office. If you still need to, you will receive the information onboard. Remember that it may take longer to receive mail or merchandise purchased online than when you are on land.
For most companies, the products will be mailed first to the cruise line’s Headquarters, then they pack in containers to send to each “port of call”, the port agents will then delivery to the ship, when it’s docked.