A BIG BUG exists in IE5 that can cause Outlook Express to delete all the files on your computer just by viewing an email message. A list of problems in Outlook Express v5 including Error Messages, Known Bugs and Workarounds and Performance Problems. By Steven Vaughan-Nichols on ZDNet. September 25, 2001. Outlook, with it deep hooks into the operating system, will always have security problems.
Outlook is vulnerable by design.
If you want all that power to trade data and code with programs like Excel and Word, security is the price you pay. Even when good users and administrators patch their software, this only closes the barn door after the horses have fled. Eudora also still has its fans and can run on Windows PCs, Macs, and even Palms. The article concludes with advice on how to configure Outlook to be as safe as possible.