I did an eval on Zimbra vs. Scalix about a year ago. I decided to roll out Scalix, because at that time, Zimbra did not support mailbox delegation, did not have a mature Outlook MAPI connector (or one at all) and required too much DEU retraining. Scalix Web Access looks just like Outlook.

Now having just said this, Scalix is a pig! It' is unstable, uses A very clunky hack of Tomcat, has no backup or restore functionaility, the Outlook connector is missing key features that Outlook/Exchange users live by, and an incident-based support pricing model that, quite frankly, is a racket. (I know packethead, tell us what you really think).

I sincerly hope Zimbra has gotten more mature and can actually put a dent in M$'s dominance.