I am very new with zimbra, just installed Network edition.

To save myself from reinventing the wheel I am sharing what I am trying to do, is it possible or has been already done?

Problem: We have a microsoft exchange server in production. The thing we want to do is to configure our zimbra server in a way:
a) All mails coming to exchange server archived on zimbra server.
b) Zimbra server synced with all MAPI features (e.g. calender, scheduling, etc) of Exchange server.
In case our exchange server goes down, a user can point his outlook/zimbra client to zimbra server and use without interruption.
Lately when exchange server comes up, exchange server sync with Zimbra and continues working. (high availability type of).

Thanks and Regards
Anuj SIngh