Trust

I have domain “A” and “B” located in two different location/subnet. These two domains are connected through VPN. I have E2K server in domain A subnet. I want users from domain B to access the E2K to retrive email and to use the public folders, whenever users from domain B access the E2K server outlook requires user name and password. I created the trust relationship but I am still unable to let users from domain B to access their email without outlook requiring credentials. It seems I need to configure some security stuff. Please help me how I can accomplish this or direct to to any resource.

Thank you,