You may notice that Outlook 2003 runs slower after upgrading the server to Exchange 2010. Users can report that deleting and moving emails between folders is slow. Users on Outlook 2007 and later will run fine. There are a number of things you can do to improve performance in Outlook 2003.
- Install Exchange 2010 update rollup 3.
- Make sure Office 2003 SP3 is installed on the client.
- If possible change the Outlook client to run in cached mode.
- On the server run the Microsoft “fix it” utility found here