Talvez seja necessário encontrar um cliente / editor de e-mail diferente se você quiser enviar tags HTML em seu e-mail: link
Microsoft Office Outlook 2007 uses an e-mail message editor based on Microsoft Office Word 2007. Office Outlook 2007 offers a WYSIWYG (what you see is what you get) editing environment. The message that you compose is converted to HTML format for sending.
Office Outlook 2007 is not designed for you to directly enter or view HTML tags when composing an e-mail message.