HTML e-mail feature in Internet Explorer 5.5 and earlier allows attackers to execute attachments by setting an unusual MIME type for the attachment, which Internet Explorer does not process correctly.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A141
https://exchange.xforce.ibmcloud.com/vulnerabilities/6306
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2001/ms01-020
http://www.securityfocus.com/bid/2524
http://www.ciac.org/ciac/bulletins/l-066.shtml
http://www.cert.org/advisories/CA-2001-06.html