“Exchange 2010 is new and different from its predecessors, unlike previous versions of Exchange, Exchange 2010 is the first designed specifically to run as an on-premises app, as a hosted service in the cloud, and as a combination of both (cross-premise). At 20 million mailboxes and growing, it's more important than ever that our understanding of the limits of Exchange be crisp,” revealed. A while ago, we began the process of documenting scalability limits of both Exchange 2007 SP2 and Exchange 2010. We've looked at all areas: things like organization sizing, rules sizing, IRM-protected messages, secure channels, named properties, load balancing, network latency, and more. Microsoft indicated that the documentation detailing the scalability limits of both Exchange 2007 SP2 and Exchange 2010 had been cooking for quite some time. The initial version of the Exchange Scale Limitations spreadsheet is currently up.
Download: Exchange 2010 Scalability Limits