I saw this on Digg this morning. I'm not a Microsoft partner, so I can't access the file, but apparently it gives a competitive breakdown of Microsoft Exchange versus Zimbra, and candidly admits Zimbra's superiority in several areas. You can see the file in the image below.
I think it does Microsoft credit that it is admitting its fallibility. What I find much more interesting is that Microsoft is taking time to position itself against Zimbra at all. After all, Zimbra has almost no market share compared to Exchange. Yet Microsoft obviously views it as a threat.
Perhaps this stems from Yahoo!'s acquisition of Zimbra. I don't know when the competitive document appeared on Microsoft's website, so I don't know whether its concern with Zimbra is a result of the acquisition or predates it.
Or perhaps it stems from Microsoft's general malaise regarding open source.
Or maybe, just maybe, Microsoft recognizes the innovation that Zimbra has brought to a stagnant email market.
Whatever the case may be, it's interesting that Microsoft would call out a newbie with a frontpage document comparing Microsoft Exchange to Zimbra. Microsoft clearly believes Zimbra is a viable option to Exchange. This should be enough to justify your company in taking a close look at this open-source competitor to Exchange.
If you have access to the document, please send it to me. I'd love to review it.