We're planning our migration from Microsoft Exchange Server 5.5 to Exchange Server 2003 and Microsoft Office Outlook 2003. For various reasons, we can't deploy the programs simultaneously. Which system should we deploy first?
In general, you should deploy Outlook 2003 first. Users will immediately benefit from many Outlook 2003 improvements, including
Users who run Outlook 2003 on an earlier version of Exchange won't get all the improvements. For example, search folders require Exchange 2003, as do server-side junk-mail filtering and remote procedure call (RPC) over an HTTP Secure (HTTPS) connection. But by upgrading clients first, you'll enable them to complete the initial full-mailbox synchronization with their existing Exchange 5.5 servers before you move the server far away. Upgrading the servers first will help the performance, stability, and functionality of your servers, so that's the appropriate choice if you're having problems with any of those things.
Of course, there are other factors to consider when you upgrade to Outlook 2003, including the cost of training users on Outlook's new features and whether you plan to do a second incremental deployment for the remainder of the Office 2003 installation. Sometimes it makes more sense to perform one deployment of all Office products instead of two separate installation phases. See "Installing Outlook 2003 Before Office 2003" (http://www.microsoft.com/resources/documentation/office/2003/all/reskit/en-us/outc05.mspx) for more information about installing Office 2003 incrementally.