Few days back new family member (Release Preview) of Microsoft Exchange has been arrived with fantastic architectural changes and new features. This is just a preview and some features may not be in RTM 
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Some of Key changes in Exchange 2013 Release Preview
- Coexistence with Exchange 2007 and Exchange 2010 is supported and Exchange 2003 is not supported. So who is still dealing with Exchange 2003 now time to migrate to exchange 2010.
- Windows 2008 R2 Operating system and Windows 8 will support as a Operating System.
- Exchange 2013 preview use new Exchange Administration Center. That has a single unified Management console that allows to manage On-premises /online or Hybrid deployments. We cannot see Exchange management Console anymore and we don’t want to wait time to load management Console.
- Reduced number of server roles. So we won’t be able to see HUB Transport server role as a separate server role. We can see only Client Access Server Role and Mailbox Server role. But still we can use Exchange 2010 Edge Transport Server role for Exchange 2013. See Mail flow diagram – Figure 1
- RPC is not longer a required protocol for Exchange 2013. Exchange 2013 use RPC over HTTPS for Outlook Connectivity.
- Exchange 2013 has introduced Data loss prevention . So you can protect sensitive data by Transport rules.
- Exchange 2013 improved the auditing functionality so we can import and export the Administrator audit log and the audit log records whenever a mailbox accessed by someone.
- With a new design We cannot see the separate Public folder database. Public folder uses Existing DAG functionality for high availability purpose. Replication method also change to single-master replication model form Multi-master replication model.
- Site Mailbox is there , So user can search document and emails by one client. This can integrate with SharePoint Server.
- Outlook WebApp has restructure. The Outlook WebApp user interface is improved and optimized for tablets and smart phones. Also user collaboration has improved. Hence users can merge contacts with social network such as Linkedin .
Figure 1
Finally, You can download Preview bits and help files:
Bits:
http://technet.microsoft.com/en-us/exchange/fp179701
CHM Help:
http://www.microsoft.com/en-us/download/details.aspx?id=30338
