Message Subject
Date/time to send message	@date_widget@ @time_widget@
Plain-text message body	<if @plain_text@ defined>@plain_text@</if>
HTML message body	<if @html_text@ defined>@html_text@</if>

The message will be sent out with MIME type multipart/alternative, with both plaintext and HTML parts, and the recipient's mail client should display the appropriate body.

If the text body is filled in and the HTML body is left blank, it will be sent as text/plain
If the HTML body is filled in and the text body is left blank, it will be sent as text/html