Well, as always with a new version of Exchange, there are quite a few
changes in Exchange 2010. One significant change is the removal of storage groups. In Exchange 2010, each database is associated with a single log stream, represented by a series of 1 megabyte (MB) log files. Each server can host a maximum of 100 databases.

Another significant change for Exchange 2010 is that databases are no longer closely tied to a specific Mailbox server. Database mobility expands the system’s use of continuous replication by replicating a database to multiple different servers. This provides better protection of the database and increased availability. In the case of failures, the other servers that have copies of the database can mount the database.

The ability to have multiple copies of a database hosted on multiple servers, means that if you have a sufficient number of database copies, you can use these copies as your backups.

High Availability Functionality

Mailbox Resiliency (Database Mobility): Exchange 2010 has been re-engineered around the concept of mailbox resiliency, in which the architecture has changed so that automatic failover protection is now provided at the individual mailbox database level instead of at the server level. Database mobility disconnects databases from servers, adds support for up to 16 copies of a single database, and provides a native experience for adding database copies to a database.

Flexible Mailbox Protection: Exchange 2010 includes several new features and core changes that, when deployed and configured correctly, can provide flexible mailbox protection that eliminates the need to make traditional backups of your data.

Incremental Deployment: Incremental deployment enables you to deploy service and data availability for all Mailbox servers and databases after Exchange is installed. (In previous versions, if you had already installed the Exchange program files on a non-clustered server and you decided you wanted a clustered Mailbox server, you had to build a cluster using new hardware, or remove Exchange from the existing server, install failover clustering, and reinstall Exchange.)

Database Availability Groups: A DAG is a set of up to 16 Mailbox servers that provide automatic database-level recovery from failures that affect individual databases. Any server in a DAG can host a copy of a mailbox database from any other server in the DAG.

Mailbox Database Copies : The high availability and site resilience features – first introduced in Exchange 2007 – are used in Exchange 2010 to create and maintain database copies, thereby enabling you to achieve your availability goals in Exchange 2010.

New Exchange Core Store Functionality

Database Maintenance: In Exchange 2010, on large or very heavy profile servers, the store mailbox maintenance task only lasted approximately 45 minutes, while ESE database maintenance usually took from six to eight hours per night to complete on large Exchange 2007 databases.

Online Defragmentation: Online defragmentation was moved out of the Mailbox database maintenance process. Online defragmentation now runs in the background 24×7. Online defragmentation is also throttled so it doesn’t have a negative impact on client performance.

Understanding Permissions

Role Based Access Control: Exchange 2010 uses the Role Based Access Control (RBAC) permissions model on the Mailbox, Hub Transport, Unified Messaging, and Client Access server roles. With RBAC, you can control what resources administrators can configure and what features users can access.

New Transport Functionality

MailTips: MailTips provide information about the messages such as details about the recipients and their availability, or reasons the message wouldn’t be delivered.

Shadow redundancy: Messages that are submitted to an Exchange 2010 Hub Transport server are stored in the transport database until the next hop reports successful delivery of the message.

Moderated transport: Exchange 2010 provides an approval workflow for sending messages to recipients. When you configure a recipient for moderation, all messages sent to that recipient must go through an approval process.

End-to-end message tracking: Exchange 2010 transport provides users with the ability to track messages from submission to the final destination.

Transport rule predicates and actions: Transport rules inspect messages for conditions specified in the rules.

Message throttling improvements: In Exchange 2010 you can configure a Receive connector to monitor the rate of message submissions by users, IP addresses, or both.

New Mailbox and Recipient Functionality

Calendaring: In Exchange 2010, your users can share information with external users. This information includes calendar, contacts, and free/busy data.

Calendar Repair Assistant: CRA automatically detects and corrects inconsistencies for single and recurring meeting items in mailboxes.

Moderated Distribution Groups: You can appoint a moderator to regulate the flow of messages sent to a distribution group. Anyone can send a message to the distribution group alias, but before the message is delivered to all participants, a moderator must review and approve it.

User-Created Distribution Groups: Exchange 2010 allows users to create and manage their own distribution groups in Microsoft Office Outlook Web App and Outlook 2010.

Permission Management for Mailbox Folders: Administrators can manage folder-level permissions for all folders within a user’s mailbox.

Personal Archive: A personal archive is a specialized mailbox associated with a user’s primary mailbox. It appears alongside the primary mailbox folders in Outlook 2010 or Outlook Web App. You can use personal archives to regain control of the organization’s messaging data by eliminating the need for personal store (.pst) files and allow users to store messages in an archive mailbox that’s accessible in Microsoft Outlook 2010 and Microsoft Office Outlook Web App.

Client Throttling Policies

Client throttling helps you make sure that users aren’t intentionally or unintentionally taxing the system. It also makes sure that users of various connectivity methods are sharing resources proportionally.

Anywhere Access

Call Answering Rules: Unified Messaging server role allows UM-enabled users to create and customize call answering rules to enhance the experience of people who call them.

Additional Language Support: All UM language packs contain the Text-to-Speech (TTS) engine and the prerecorded prompts for a specified language and Automatic Speech Recognition (ASR) support.

Voice Mail Preview: In Exchange 2010, the Unified Messaging server role uses ASR on newly created voice mail messages. When users receive voice messages, the messages contain both a recording and text that’s been created from the voice recording.

Outlook Web App enhancements: Outlook Web App mailbox policies can be used to control users’ access to features in Outlook Web App. More browsers and IRM protected messages are now supported in OWA. Conversation view, Chat (without having to install Office Communicator 2007), more actions in the right-click menus and the ability to attach messages to messages are other enhancements.

Text Messaging Features: Missed call and voice mail notifications, Calendar and agenda updates can be sent as a text message.

Discontinued Features from Exchange 2007 to Exchange 2010.

Storage groups Exchange 2010 uses database copy functionality.
Clustered mailbox servers
Cluster continuous replication
Local continuous replication
Standby continuous replication
Single copy cluster
Exchange 2010 uses DAGs and mailbox database copies.
Setup /recoverCMS Exchange 2010 uses Setup /m:recoverServer.
Client authentication using Integrated Windows authentication (NTLM) for POP3 and IMAP4 users NTLM isn’t supported for POP3 or IMAP4 client connectivity. Connections from POP3 or IMAP4 client programs to Exchange 2010 will fail.
Move-Mailbox cmdlet set Use move requests to move mailboxes.

A complete description of the features can be found at http://technet.microsoft.com/en-us/library/dd298136.aspx.

– Thanks, Jinesh.