This may not help you but if you are using McAfee Virus Scan 4.5 or 6 I found an issue for this on Microsoft. This is the link. I hope it helps.
OS is WIN XP. Using Outlook Express for mail. From time to time I find all my mail boxes have been emptied for no reason that I can discern. Very frustrating when one wants to reply to a previously received e-mail. Have tried to duplicate this problem every way I know how to but cannot do so. Have sent report to Microsoft over two weeks ago with no reply. Would this be some form of virus or worm? More important, how can I cure the problem?