There's a lot more to Exchange than just email. Shared tasks, calendaring, and folders. Sounds like the OP is looking for Exchange hosting.

Mail2Web offers such a plan, but as I don't use Exchange I don't really know what it entails. You may want to take a look.

Other than actually using Exchange, I think Scalix is about the only mail system out there that offers anything close to complete Outlook/Exchange compatibility, but I don't know of any Scalix hosts.