I am changing my email templates and I want them to be send as HTML. I write directly the code into the Body element of the concrete template - lets say "New Member". I write it without any escaping, directly:
I test my html code and embedded css in index.html file locally on my machine and test it in some browsers. Then I copy the code in the body of the message template but it does not works.
The message templates are html by default. The opening and closing html and body tags are already defined within the core code that generates the messages.
If you have additional html that you want to include in the message template, then Nic's suggestion above is how to achieve it. Simply open the message template in admin area to edit it. Then click the tools menu in the editor and choose Source Code. Put your html in here with no body, head, or html tags.