The problem is that most of the 'exchange alternatives' I've seen are written by people who essentially think "Exchange sucks, we just need to throw together some imap and some caldav and... then profit"
I think a better exchange alternative would be written by people who _love_ exchange, but just think it could be cheaper or do *x* better than it currently does.
And MS have done a lot of good work in this area that needs to be caught up with: Microsoft's EAS protocol has actually become something of a de-facto standard for a lot of mail systems that want to connect to smartphones and tab…