Outlook 2000 auto clearing e-mails

Several machines running Windows and Office 2000 on our network have begun to automatically delete E-mails from Outlooks folders. I have checked the maintenence settings and disabled the cleanup operation. However the mails are still being deleted. At the momment I’ve had to get Outlook to leave a copy on the server but this means that it brings down old mails all the time. Has anybody else experienced this or come across a soloution.