If you really like an email you received from Uber, Pizza Hut, JustGiving, whoever... you can use a cool and free service called Scope from Litmus. You don’t need to pay for a Litmus account to use Scope. https://litmus.com/scope/
Using the free Scope bookmarklet takes a few seconds and displays the HTML code of that email you love so much.
Just copy, add a new template, select "Paste in HTML to create a Classic Template", and paste in the HTML to create your new template.