From last 3 years we are using Zimbra open source edition for internal user's mail communication and Exchange for our customer. Now management is planning that we should go for zimbra network edition to serve mail service to customer. So in future MAPI request will get served from Exchange and IMAP and POP3 requests will get serve by Zimbra..
Now in this case domain should be same for Exchange and Zimbra and both should be in primary mode for respetive users base on client protocol.

I searched on internet to get details to setup such configuration but not getting any straight forward solution. Can anyone please help to provide some clarity on the configuration part at DNS and MTA level.