Gartner: Microsoft E-Mail Momentum Growing at IBM's Expense

I do apologise for yet another link to a paid for Gartner report, but some preview clippings say it all... (please forgive me for highlighting and underlining)

Client inquiries indicate that Microsoft is gaining momentum in the e-mail and calendaring market, and the trend appears to be accelerating. Users should focus on business requirements, not just vendor marketing claims, when making technology decisions.

Source : Gartner.com