|Feature||Exchange Server 2003 Standard Server||Exchange Server 2003 Enterprise Server||Exchange Server 2007 Standard Server||Exchange Server 2007 Enterprise Server||Exchange Server 2010 Standard Server||Exchange Server 2010 Enterprise Server|
|Database Storage Limit||75GB||None||16TB||16TB||16TB||16TB|
|Single Copy Cluster||No||Yes||No||Yes||No||No|
|Local Continuous Replication||No||No||Yes||Yes||No||No|
|Standby Continuous Replication||No||No||Yes||Yes||No||No|
|Cluster Continuous Replication||No||No||No||Yes||No||No|
Keep in mind you also need client access licenses or CAL’s. The are sold in standard and enterprise edition. The enterprise however is just an add-on to the standard license. So for one enterprise user you must have a standard CAL and enterprise CAL. The main difference between the two is unified messaging which enterprise gives you the rights to.