Outlook Express 6.00 allows remote attackers to execute arbitrary script by embedding SCRIPT tags in a message whose MIME content type is text/plain, contrary to the expected behavior that text/plain messages will not run script.
https://exchange.xforce.ibmcloud.com/vulnerabilities/7118
https://euvd.enisa.europa.eu/vulnerability/EUVD-2001-0981
http://www.securityfocus.com/bid/3334