First, IE6 isn't really a mail program. It is a browser. Which mail program are you using?
Regardless, check your settings in your mail application and check to see if there is an option to disabled html email or disable graphics. If they are checked, uncheck them.
If you have mistakenly stated email when you mean all web pages show with the red x instead of the graphics, then that is not a mail problem at all and is a problem with IE. If IE is the problem, go to Control panel, Add/remove programs, find IE, click Add/Remove with IE highlighted and select Repair.
You should try to reinstall the applications (mail or IE) if that fails.