As usual I recommend you all to please refer the TechNet for indepth and accurate knowledge.
Below are the major changes which have been introduced in Exchange 2010 and would like to share some.
Outlook Web App
The most visible improvement for end-users is Outlook Web App (previously known as Outlook Web Access).
To name a few: Favorites, Search Folders, attaching messages to messages, integration with Office Communicator, a new Conversation View (which works very well!), integration with SMS (text) messages and the possibility to create Outlook Web Access policies, which give the Exchange organization administrator the ability to fine-tune the user experience
The Exchange Server 2007 Cluster Continuous Replication (CCR) and Standby Continuous Replication (SCR) features are now combined into one new feature called Database Availability.
With Exchange 2010 we no longer have the concept of LCR, SCC, CCR and SCR. But to be more precise only LCR & SCC is been removed from Exchange. CCR and SCR is now combined and evolved into a High Availability framework known as DAG. It supports local or site level highly available and disaster recovery solution. You could only protect your mailboxes with DAG in Exchange 2010.
DAG uses the cluster database, heartbeat and file share witness functionality, previous exchange were an application which relied on windows failover cluster where in case of 2010 it is not.
With previous versions of Exchange when configuring CCR you could not install other exchange roles, but with DAG a mailbox server part of a DAG can have other Exchange roles too. DAG can now be managed via EMC instead of using cluster management tools which previous version of exchange was used. There is no storage group concept, now database has been moved to organizational level
Database in Standard is 5 and in Enterprise are 100. Public store database are not supported by DAG. Windows 2008 with SP2 or R2 Enterprise is required to configure DAG in exchange.
Exchange core store functionality
Compared to Exchange Server 2003, Exchange Server 2007 dramatically decreased the I/O on the disk subsystem (sometimes by 70%). This was achieved by increasing the Exchange database page size from 4KB to 8KB and by using the 64-bit operating system. The memory scalability of the 64-bit platform makes it possible to use servers with huge amounts of memory, giving them the opportunity to cache information in memory instead of reading and writing everything to the disk.
One of the design goals of Exchange Server 2010 was to use a single 1TB SATA disk for the mailbox database and its log files. Another goal was to allow multi-GB mailboxes without any negative performance impact on the server. To make this possible, the database schema in Exchange Server 2010 has now been flattened, making the database structure used by the Exchange Server much less complex than it was in Exchange Server 2007 and earlier.
Exchange Control Panel
It is now possible to perform some basic Exchange management tasks using the options page in Outlook Web Access; not only on the user’s own properties, but also at an organizational level. With this method, it is possible to create users, mailboxes, distribution groups, mail-enabled contact, management email addresses etc.
Active Directory Rights Management
With Exchange Server 2010, new features have been added to the Rights Management Services, such as:
Integration with Transport Rules – a template for using RMS to protect messages over the Internet.
RMS protection for voice mail messages coming from the Unified Messaging Server Role.
Transport and Routing
Exchange Server 2010 also offers (at last) enhanced disclaimers, making it possible to add HTML content to disclaimers to add images, hyperlinks, etc. It is possible to implement cross premises message routing.
Transport servers in Exchange 2010 (both Hub Transport and Edge Transport servers) have built-in redundancy to protect against the loss of messages in transit.
A safe copy of each message is retained until the message is successfully delivered to the next hop; so if a queue ails, there is a backup copy on another transport server.
This is the one of the feature I liked very much.
Exchange Server 2010 now contains a personal archive; this is a secondary mailbox connected to a user’s primary mailbox, and located in the same Mailbox Database as the user’s primary mailbox. Since Exchange Server 2010 now supports a JBOD (Just a Bunch of Disks) configuration this isn’t too big a deal, and the Mailbox Archive really is a great replacement of (locally stored). With SP1 i heard the secondary mailbox path can be changed to different database.
MAPI is accessed through CAS
Previous versions of exchange outlook client using MAPI used to connect mailbox server role, with Exchange 2010 outlook client uses CAS to connect their MAPI request too.
How it works?
On each CAS server there is a new service called MSExchangeRPC which runs as Microsoft.Exchange.RpcClientAccess.Service.exe and listens on port 6001 for HTTP connection and uses dynamic ports by default for tcp/ip connections.