Just noticed that many of my Outlook XP machines (using Windows XP with SP2) are really slow in sending and receiving messages. I checked all the normal settings which are:
Exchange Server 2003
In the options, I have the email set to send immediately when connected and then to 1 minute to do an automatic send.
I can logon with the same users to a machine that has Outlook 2003 and the messages disappear immediately.