In CubeCart's administration backend, on the left navigation panel, click Email Templates.
The Email Contents tab is a list of all the main contents of CubeCart's emails - click the flag of the language you wish to edit.
The Email Templates tab is a list of the email's overall common content - click the Edit icon of Default Emails.
On the page that is now shown, click the HTML Content tab. (Do Not Edit Anything. Possible bug here.)
Hover the mouse over the blue squares to see a tooltip as to what protected content is here.