You don't need a special address to
contact someone on a given ship.
What they provide is an Internet
connection from where any user on
the ship may access his/her already
existing mailboxe on some provider
server (yahoo, hotmail,sprynet (in your case)).
Idealy the passenger should contact you first from the ships internet center. If a passenger signs up at the internet cafe they are given an adress. If you do not have this adress I do not think that you can send an e-mail to a passenger. It might be an idea to call HAL in Seattle on 206-281-3535 for advice.
Regards, Leslie a fellow traveler.