Outlook Express 6.0 HTML E-mail help

I have a client who uses OE 6.00.2900.3028

He doesn’t seem to have problems with any HTML e-mails except the ones that I send to him. When he receives mine, they show up as the HTML code

I have had him make sure the checkbox that says “Read all messages in plain text” is not checked. Also under View he cannot choose “Message in HTML”

Any help is appreciated. Thanks