per the migration instructions:

Setting Up Shared Domain with Exchange
You can set up a domain that is shared by Zimbra and Exchange with some users on the Exchange server, and other users on the Zimbra server. There are several potential ways to do this. The best way for your deployment depends on your site’s configuration, IT policies, and other conditions.

[add zimbra's url as this kept getting blocked for spam when I had the www and http ect ect]

How would this work exactly is there any documentation on a setup for this?

Thanks for time.