Such a program would be capable of taking any action that the user himself could take on his machine, including adding, changing or deleting data, communicating with web sites, or reformatting the hard drive. Also, the vulnerability could not be exploited if File Downloads have been disabled in the Security Zone in which the e-mail is rendered. This is not a default setting in any zone, however. This has the effect of preventing e-mails from being able to automatically launch executable attachments. Multipurpose Internet Multimedia Extensions or MIME type is a code that specifies the content type of a multimedia file.
Mail clients handle creating, sending, receiving and displaying e-mail.
Rendering is the of processing and displaying a web page. HTML mails are rendered by IE because they are essentially web pages sent as mails. The flaw in this case involves how IE renders HTML mails.