Exchange open source alternative

All

I am looking at potentially moving away from exchange, at the moment I am on exchange 2003 x 2 servers, and 90 staff

I have read this thread:
http://community.spiceworks.com/topic/121789-open-source-alternatives-to-exchange-server?started_from=new_topic

and wondered whether there is anything else on the market that is recommended? I'm looking for:

Outlook connectivity
Sharing of calendars
Blackberry 10 connectivity
Journalling
Integration with AD(?)