Earlier this week I already posted some information by MarketCap with regards to the marketshare of the major Groupware solutions. This research shows Microsoft leading with 65,1 % marketshare.
The following article is somewhat older (November 2004), but shows a similar picture and also includes the marketshare in the various vertical markets. Although the text in the Article is in Dutch, I think the grpah shows all the relevant information; in particular Microsoft’s position over Lotus Notes and Novell Groupwise.
The source for this article is the Automatiseringgids of November 12, 2004. Source for the research is MarketCap and Computer Profile.