Is it possible to migrate from Exchange 2007 to Zimbra 4.5.6. In our offices we currently run Exchange 2007 together with Outlook 2007.

To be able to use the Outlook Connector it would be an option to downgrade to Outlook 2003, but downgrading the Exchange Server only to migrate the mails, calenders and so forth is not an option. Besides that, I don't know if this is even possible ;-)