I am planning to co-exist Zimbra with Microsoft Exchange 2010. Requirement is send and receive emails between Zimbra and Exchange. GAL Sync. Free-Busy.
And there will be separate mailboxes for the two different mail servers.

Zimbra mailboxes

user1@domain.com
user2@domain.com
user3@domain.com

MS Exchange 2010 mailboxes

user4@domain.com
user5@domain.com
user6@domain.com

For example the mails send to user1, user2 and user3 should go to Zimbra Server and mail send to user4, user5 and user6 should go to Exchange 2010 server.
I have configured the Exchange Server to send email to Zimbra when the mailbox is not in the Exchange 2010 Server. Now I need to configure Zimbra to send email to Exchange when the mailbox in Exchange. Please assist me on this regard.
Also I need kind help on GAL Sync and Free/Busy.

Thanks,
Damitha