Exchange server 2003/2007 "branch cache" ?

Hello.

I have the following scenario :
9 Vessel's with MailDeamon as mail server on each vessel.
Clients with outlook.
Each vessel has it's own domain, 2003 AD.

I want to do the following :
Replace this MailDeamon with either exchange 2003 or 2007 on all vessels.
We want the mail to be replicated from all vessels/domains/exchangeservers to 1 central exchange server in our HQ.
Do we have to have 1 exchange server onboard each vessel or is there a "server-cache" option that can replicate and take care of mail? (Not thinking about cached mode).
I mean that we can have 1 main exchange server handling all mail from all domains and 1 "cacheserver" on each domain?
Or is the best way/only way to have 1 exchange server on each vessel wich then connects to the main exchange server and replicates.
And can the central exchange server at our HQ handle upto 9 different mail"domains" ?

I am not that good at explaining what I want here. Ask questions if anything is unclear :)