Exchange Server 2013 CU1 or later (not RTM) supports co-existence with the following previous versions of Exchange Server:
- Exchange Server 2010 SP3
- Exchange Server 2007 SP3 + update rollup 10
There will be no co-existence support for Exchange Server 2003. If you're still running Exchange 2003 and are looking to upgrade to Exchange 2013 you'll need to do an interim upgrade to Exchange 2010 (or 2007) first. I recommend an upgrade to Exchange 2010 instead of 2007, as it makes for a better upgrade experience to Exchange 2013.
Active Directory Requirements for Exchange Server 2013
Exchange 2013 support a Windows Server 2003 Forest/Domain functional level, and Windows Server 2003 SP2 domain controllers.
A schema update will be required as usual, and this is part of the same service pack/update rollup that is required for co-existence support.
The Upgrade Process for Exchange Server 2013
The high level documentation and general guidance for Exchange 2013 upgrades has been published at the Microsoft Exchange Server Deployment Assistant.
For more detail on the Exchange 2013 upgrade process you can follow my article series here:
Many of the challenges in these upgrades come not from Exchange itself, but more from the integration points such as third party software. In that respect you will need to watch for announcements from the vendors for products such as your backup software.
Client Support for Exchange Server 2013
The following clients are compatible with Exchange Server 2013.
- Outlook 2013 (15.0.4420.1017)
- Outlook 2010 Service Pack 1 with the Outlook 2010 November 2012 update (14.0.6126.5000).
- Outlook 2007 Service Pack 3 with the Outlook 2007 November 2012 update (12.0.6665.5000).
- Entourage 2008 for Mac, Web Services Edition
- Outlook for Mac 2011
For more information on discovery of client versions in your environment see the following article:
There is no support for Outlook 2003. If you're still running Office 2003 in your environment and intend to upgrade to Exchange 2013 then you will need to upgrade Office first.