It is now possible, and rather easy, to copy email and letter templates.
In both cases, the procedure is simple. Under the Configuration menu, go to either letter templates or email (a.k.a. multipurpose) templates. From the list, choose the new link that says Copy.
The system will duplicate the document, appending a -copy to the name. You can then edit the document as usual.
Here’s a short video showing the feature in action.