HI Robin,
hope all is well
well i tried to think out of the Cisco box, but it seems others have configured this and failed in the email integrations. check the link below:
https://supportforums.cisco.com/thread/2077406
since this is not listed in the compatibilty matrix it's not supported by cisco, or at least not tested by the BU. but in the above thread, they managed to add an exchange server inbetween. hope this helps.
cheers
Zaid