Now and then a message in my Windows Mail Inbox has garbage like "<!--[if !supportLists]-->·          <!--[endif]--" at the beginning of each line. When informed, the sender suggests that my Windows Mail Options are not set for HTML. Under the Read tab, my options include a checkbox labeled "Read all messages in plain text". That box is NOT checked. My default encoding is Western European. Under the Send tab, "Mail sending format" has the HTML box checked. How can I get such messages to display correctly?

I operate under Microsoft Windows Vista Home Premium SP2 with Windows Mail v6.0. The latest message with such garbage came from a person who uses Thunderbird as a mail client.