Applicable to Outlook Express Version 6.x - Problem, OE will not allow opening of attachments including Digests of mail lists.
1. Open Outlook Express
2. Click on "Tools" and then "Options".
3. Click the Security tab
4. Under Virus Protection, click to remove the check from the box labeled "Do not allow attachments to be saved or opened that could potentially be a virus".
5. Click OK
Use caution if you receive emails from others with an attachment. Unless you are expecting or have verified the attachment with the sender, right click and either scan with your virus scanner (if it allows) or save to the desktop and scan it at that point. Most Anti-virus software will allow single file scanning by right clicking on that file.
Thanks to several contributors for this information.