Outlook 2002/XP MS Mail Not supported

Microsoft Support state that Outlook 2002/XP does not support MS Mail! Our standard configuration for clients we install systems for is to use a Postoffice on a server and Outlook with MS Mail on client PC's. However during a recent testing session of Offcie XP we noticed that MS Mail was installed and working. But due to a reconfg of that PC we are unable to reproduce it at the moment. We have had to put Outlook 2000 onto an Office XP installation to get round this but I would like to hear from you if you have a tested workaround.