I can now confirm that Zimbra sync works with the latest .51 firmware -- sort of. This firmware version added support for Exchange 2003. Now with N900 and this new firmware, MfE and Zimbra backend: - E-mail download works fine. - Calendar sync works fine both ways. Tasks don't work fine and cause the whole sync process to fail with a communications error ("Error in Exchange server"). Despite this error, e-mail and calendar is synced as stated above. I have not tried contacts sync yet. As far as I can see, there is no way in the GUI to disable tasks syncing, so we have to live with the occasional error popup. Although the sync seems to flash the error message frequently when it fails.