For the past couple of years, Microsoft has been fixated on beating IBM Lotus Notes/Domino in the e-mail server market. But according to a Yankee Group report that will be published next month, the real threat to Microsoft Exchange isn't IBM — it's Linux- and open-source-based e-mail servers.

Yankee will publish in April its "2007 Global Server Hardware and Server OS Survey." The survey of nearly 1,000 IT managers and C-level executives includes some "ominous" news for Microsoft, according to a copy of the executive summary of the study that I had a chance to see this week.

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