If you need to migrate Google Apps to Zimbra here is a simple howto. Just follow the steps and you will have your Google Apps mails transferred to your Zimbra mailbox.
Migrate Google Apps to Zimbra - VIONBLOG
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How to Migrate Zimbra to Google Apps ? Complete Solution
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How to Migrate Zimbra to Google Apps ? Complete Solution
Zimbra to Zimbra Migration - Zimbra :: Tech Center
How to Migrate Zimbra to Google Apps ? Complete Solution