I am trying to setup zimbra trial in a split domain environment.

I am following the split domain wiki. My question,

If exchange server is the primary and zimbra is the secondary, how do I configure exchange to forward mail to the secondary zimbra server for users hosted there? I read on another post that they configured the exchange smtp connector, any help appreciated. A step by step would be greatly appreciated for this task and how to do the split domain setup between exchange and zimbra.