I think Yahoo paid quite a bit more for Zimbra in the first place, so looking at only that for valuation, that would seem a good discount for VMWare. But yes, the numbers are unreal seeming !
The number we know is the original VMware valuation, which was ~$350M. The number we don't is the price this time around, because financial terms weren't disclosed. It seems safe to assume, however, that VMware is paying less, and AllThingsD's reporting validates that.
Sorry, that should read "the original Yahoo valuation..."
Yes, I knew what you meant ;) I think an open source exchange killer was far more up the list of priorities when Yahoo bought it, than it would be today. (Exchange is still everywhere, but people don't seem to mind nor talk about it - with Lotus, and Google "gone google" in the market - maybe people view it as acceptable competition now?)