As of about 6 months ago I couldnt get this working properly with clients on BIS and using OWA. Some users it would work well, but others it would not.
As far as I know BIS is not really setup to reconcile messages in the way you are after, at least not the last time I checked and we never really got any of our clients (approx 30 different companys) working in this way.
I could be wrong though!
I would be interested to know the full story myself.