...
The Message html field has a WYSIWYG editor attached to it. The editor is activated by clicking the 'Toggle WYSIWYG editor' link above the text area. 
Email Template Message Html WYSIWYG editor link
The WYSIWYG editor is used throughout UltraCart.com, and is useful to create html blocks. Clicking the toggle link will display buttons on the top of the text area and the editor will render your input as html.
...
View After Previewing & Saving
Previewing the Email Template
The Validation & Preview button, when clicked, will also populate an iframe in the Preview tab displaying your rendered html code.
Some rules about the preview tab:
...