I like the idea presented in this wiki article
Split Domain - Zimbra :: Wiki
and I get how to make zimbra the primary but what about doing this with Groupwise(GW) 7 as the secondary that I'm migrating away from. I'd like to make Zimbra my primary mail handler and switch users from the Groupwise 7 server as I'm able over the coarse of a few weeks. I've setup Zimbra to forward all mail to the GW server but once I switch the a user to zimbra, how do I get GW to send mail to a zimbra user (email@example.com) from a user still on the secondary(firstname.lastname@example.org? I can't seem find any references to user routing or forwarding for GW.
I've had experience with Postfix and there are docs for Zimbra but I have no experience with GW server and I'm not even sure what this function/feature would be called.
Can anyone point me in the right direction on this?