Migrate from Exchange to Zimbra

Change mail routing

First create all currently existing Exchange email accounts in MailWall. Then in 'Delivery Options' disable 'SMTP Forwarding'. Once it's accepted within next 5 min. new emails will start coming to Zimbra accounts

Import legacy data from Exchange to zimbra

In order to get email, contacts, calendars imported to Zimbra first for each account on Exchange export the data to .pst file.

Then just import the .pst files following this article:
http://helpdesk.ieinternet.com/help/index.php/Import_pst_to_Zimbra_accout