Exchange 2003, single forest multiple domains

Hi all, I have an exchange 2K3 sever in a forest with multiple domains. Can I use his server for all of my accounts in the multiple domains? When I create a new user that is not in the domain of the server, the wizard gives me the choice to create a mailbox, it also confirms that the mailbox has been created, but I am unable to see any email addresses in the property of the user!
I have forced replication and RUS rebuild and update.
Any help?
Tnx, J.