help exchange /sbs

Hi

I’m currently have exchange running on sbs, we are trying to setup a new domain using win23k domain controllers and seperate excahnge box. Trouble is I can’t move everyone over to new domain just yet, I was going to setup a trust between sbs server and win23k server but just found out you can’t do that. How can I setup so that users in sbs domain can access new email account in win23k domain. Please help!