This one can back up to Lotus cc:Mail vs. Microsoft Mail, two early e-mail systems finding their way in a new world called LAN-based communications. While cc:Mail had a devout and passionate following, which formed an angry mob at their annual user conference when the death of the product was announced, the real arguments didn't start until Notes and Exchange emerged from the ashes.
Eric Arnum, who was the Ernie Pyle of the early Notes/Exchange wars with his now-defunct Electronic Mail and Messaging and Messaging Online newsletters, tabulated seat counts from the trenches for a captivated audience. Installed base numbers and arguments over who had the best implementations of the latest Internet protocols have now disappeared into real-time communications bundles where Notes and Exchange are but a piece of a larger whole in their respective platforms.
Still today, Notes users remain the most passionate, clubbing IBM back into line each time Notes wavers from the center. Exchange, once anointed the leader of Microsoft's unified communications caravan, now is just one part of it. But this is an argument with two winners. Both platforms deliver rich revenue streams for their respective companies that would make small countries blush.