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.
NOTE: Scope is free but only works in Gmail and the Chrome browser.
How to use Scope: ➡️ Go to the web page https://litmus.com/scope/ and ➡️ drag the orange button into your Chrome bookmarks bar. Next, go to Gmail and ➡️ open the email. Now ➡️ click on that Scope booklet and you can see the email and select the 'code' to copy. You now have your HTML, and so back to Step 3 in How to convert linked stylesheets to inline above.
