Creating a summary of contents on civil mailings
There isn't an automatic feature but this is what html anchor tags do. See https://developer.mozilla.org/en-US/docs/Web/HTML/Element/a#Linking_to_another_section_on_the_same_page

So at the top of your html mail you can put

&lt;a href="#thing1"&gt;Thing 1&lt;/a&gt;

and repeat for each title/summary, and then use the id in your stories lower down like

&lt;div id="thing1"&gt;Here is the actual story.&lt;/div&gt;