Strange Problem

Here is a strange one for you. I have a user here who has a problem with the text encoding in IE and Outlook. If he gets a message sent in HTML format or Opens a webpage that does not have a font specified in the code, it shows up like upside down characters and squares. If he changes his encoding in IE to Thai, it shows up normally. I have tried everything to fix this problem. Anyone know how to fix this or have you ever seen it before. If you need more detail, post a reply and I’ll give you all the info I can.