Good morning Merijn,
it's an interesting idea. But I'm not sure you will get a concrete answer from Zarafa concerning the licence issues, as long as there is no concrete statement from MS.
I like the last comment of John Gordon (in http://notes.kateva.org/2009/02/googles ... sting.html
), as MS shows real interest in "going open" during the last months.
Are you thinking of an implementation within the open source or commercial version?
Thanks, best regards,