HTML not sending on Mail Merge

I am trying out the regular version of Mail Merge before possibly buying premium, but I am unable to send HTML mail.

I have gone into the HTML WSYWIG to which you link, and gotten this HTML:

Write HTML Mail

Use this WYSIWYG HTML Editor to compose and send rich-text HTML emails with support for tables, images, hyperlinks and other formatting styles not available in your email program.

Advanced users can switch to the HTML view and directly edit the HTML source of the message or apply their own custom CSS styles to any of the elements.

(I hope that shows up as plain text and not as formatted HTML)

I paste that in the BODY field as instructed, but when I get the e-mail test I’m sending it is unformatted. It shows me all the HTML tag elements rather than formatting the HTML.

Can anyone help with this?