So another set of common questions I get is “Do I need to run Outlook 2010 after I migrate to Exchange 2010?” or “What don’t I get if I’m still on Outlook 2007 in an Exchange 2010 environment” or “Can I still use Outlook 2003 against Exchange 2010?” or “Which Outlook 2010 features work against an old Exchange 2003/2007 Environment?” Here are answers to these and many other similar questions…
Do I need to run Outlook 2010 after I migrate to Exchange 2010? / Can I still use Outlook 2003 against Exchange 2010?
Simple answer, NO, you do not need Outlook 2010 to use Exchange 2010 and in fact if you transition from Exchange 2003 or Exchange 2007 to Exchange 2010, if you use the migration tool to move your mailboxes to Exchange 2010, your Outlook 2003 or Outlook 2007 users won’t even know you moved them to Exchange 2010. Exchange 2010 still supports MAPI access and Outlook Anywhere (RPC/HTTPS) to Exchange, so when a user’s mailbox is moved to Exchange 2010, the user still keeps their old Outlook 2003 / 2007 client.
Note: the trick during the migration process is after you “move” a user’s mailbox from Exchange 2003 or Exchange 2007 to Exchange 2010, keep the old 2003/2007 server running for a couple weeks. The next time the user launches Outlook, their Outlook profile is still configured to point to the “old” Exchange 2003/2007 server. But if you keep the old server online, when Outlook tries to connect to the old server, the old server will tell Outlook that the user’s mailbox has been moved and it’ll tell Outlook to automatically update the Profile to now point to the new location of the user’s mailbox (ie: the new Exchange 2010 server). After a couple weeks you’ll find most (90%+) of your users will have launched and run Outlook and their profiles will have automatilly changed meaning NO admin intervention to update the users profiles. You can now uninstall the old Exchange 2003/2007 server, however you’ll have a handful of users whose profiles will not have switched over if the users were out on extended leave and hadn’t connected to Outlook in the couple week period you had the old Exchange server running (for these users, you just go into their Outlook profile and point them to the new Exchange 2010 server)
Back to Outlook 2010 though, so you can most certainly use older version of Outlook against Exchange 2010. The users will get all of the features that the version of Outlook (2003/2007) they are running. Microsoft does not officially support Outlook prior to 2003 against Exchange 2010, so Outlook XP, Outlook 2000, etc are “not supported”.