Some days ago Zimbra announced that has crossed the 40 million user mark. In some reports recently appeared on the web (see venturebeat.com and mediapost.com) is reported that Google has 11 million users, far away from Zimbra. A note also appeared on Google Press Center at the beginning of 2009.
How about Lotus Notes? Well I quickly searched over IBM Press room and I found this press note:
IBM Lotus Notes and Domino has grown to 140 million licensed users worldwide, has increased its user base across small- and medium-sized businesses, and is used by more than half of the largest 100 corporations in the world, and 80 percent of the top 10 global companies in banking, telecommunications, aerospace and defense, consumer products, electronics, insurance and pharmaceuticals.Far away from Zimbra and Gmail.