Thanks for the comment and the question, Jerome. To answer your question, I would estimate that 80-90%+ of my customers view email as a mission critical application. The majority of the customers I work with have more than 5,000 seats and I’ve found that the larger my customer, the more they rely on email. In fact, since it was released, I have never deployed Exchange 2010 for a customer who did not utilize Database Availability Groups for hardware or database redundancy in some fashion. While I think this is partially due to the improvements Microsoft has made within the product, I think the larger factor is that many organizations rely on email for critical business processes in addition to daily communication. Because of this, an email outage can not only cause lost productivity, but potentially lost revenue. As more organizations realize how dependent they are upon email, they classify it as a mission critical application and design a solution to meet their needs.