How're y'all doing today?

Here's how it is. I have two Zimbra 4.5 servers OE running, the main server replicates to the backup every night at 12 am. I want to test Zimbra 5 on the backup server before I go live.
Is it possible to replicate from Zimbra 4.5 to Zimbra 5?

Please, urgent response would be appreciated

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