I am a school district and we give email accounts to most of our students. For 95% of our accounts the Open Source Edition will fit our needs perfectly, but for our principals and administrators they want some more advanced features, ie iPhone sync, outlook etc. I have sendmail running at our gateway doing all anti-virus/anti-spam and currently we use those servers for the smtp server for all email and I use alias files there to direct email to the backend mail store.
The problem that I seem to be having with Exchange/Zimbra integration is the calendar availability/scheduling needs to be able to happen across servers, and getting email to go from an Exhcange account to a Zimbra account. I have read some of the posts and documentation on this, but they seem to assume greater AD/Exchange knowledge than I currently have. Does anyone have any more detailed documentation?