We are trying to setup zimbra to share the same domain as our exchange server. I have followed the instructions here to setup exchange to share the domain. That allowed my exchange server to relay any addresses that it didn't recognize to my zimbra server.

At this point I can receive inbound mail from external users and exchange users to my zimbra server, but zimbra won't deliver mail to exchange. I am sure that it is something simple, but I can't seem to figure it out.

When I try to reply to a message sent to a zimbra account from an exchange account I get the following error:

msg - Message not sent to any recipients because of these failed addresses: 
Robert <RobertJ@domain.com>
code - mail.SEND_FAILURE
method - ZmCsfeCommand.invoke
detail - soap:Sender
Any help would be greatly appreciated,