A few of the missing features that are available in Exchange Server 2003 or 2007 are:

• Storage Groups and Recovery Storage Groups are removed and the concept of mailbox database and Recovery mailbox database is available
• STM database has been removed, so it's just moved to EDB database as like exchange 2000 and the STM database concept is incorporated with EDB database
• ADMINISTRATIVE Group and Routing Groups is been completely removed. Routing Groups are replaced with Active Directory SITES and services to define organizational Sites and routing of messages to those sites
• EXOLEDB, WEBDAV, CDOEX and the Store Events are gone; exchange 2010 uses the new Exchange Web Services as the primary method to provide web services to client system
• Public Folders are still announced in a de emphasized state
• Other features like front and BACK end architecture has been removed, New Management tools EMC and Exchange Management Shell are introduced.
• Normal Permission Model is replaced with powerful or granular permission model named Role Based Access Control

A few of the missing features that are available in Exchange Server 2003 or 2007 are: