Customize the “read more” link: thru shortcode or code or..?

Hi all,
I’m trying to configure a newsletter sending the last posts published on my (future) site., with a twist: I would like to customize the url each item points to, something else than the post’s url: I’d set this url to a “mailto” link with the post title as subject.

The AutomatedLatestContentBlockModel as a “readMore” attribute that can be either a link or a button.
By default, this readMore component’s url attribute uses (what seems to be) a shortcode [postLink]

`readMoreType: ‘button’, // ‘link’|’button’
readMoreButton: {
text: ‘Read more’,
url: ‘[postLink]’,
}

I am clueless so far about the way I could achieve my goal, probably because of my global lack of knowledge.
I didn’t manage to find out whether the shortcode/keyword “postLink” is a part of the WordPress core list or mailpoet’s list. It has to be from either of the two sets, right?
Or, could this code be “something else”? In which case, would that mean that I’d have to find another way, possibly by hacking/overriding the code handling the newsletter’s content generation, somehow?

Please forgive me if the question is trivial and the answer so obvious it’s not the worth the time you’ll spend writing it down.
Sorry if my question is too much on the “custom dev” side rather than the “core” side. Wouldn’t it be cool, though, if one could choose the url from the latest content bloc configuration 😉 ?. In which case, any ounce of help will be even more appreciated.

Thanks!
And cheers,
Zack