What do you mean exactly? Are you expecting the text itself to be transformed in to html, or are you emitting html and you're expecting whatever you're using to send email to automatically recognize that it should tag the message as html?
When I am in OUTLOOK, I can type text into the e-mail. I can then highlight some of that text and click the B (bold) I (italic) or U (underline) icons and the highlighted text becomes BOLD, ITALICS or is UNDERLINED.
When I send the text of the e-mail from ACCESS, when OUTLOOK opens up, the B, I or U icons are greyed out.
To get the icons back and working, I have to click the combo box in OUTLOOK and change the text from PLAIN TEXT to HTML. I can then highlight the text and change whatever I want to BOLD etc.
I want to miss out the stage of having to change the text in the mail from PLAIN TEXT to HTML.
My gut feeling is that you can't specify HTML with SendObject, though I could be wrong. The HTML you've specified is for the output format of the attachment, not the body. I think you'll need to use automation: