I outlined this in https://wordpress.org/support/topic/shortcode-for-excerpt-for-preview-text/#post-17318675, but to copy-pasta here:

Because I have a header in my email, the preview text is not the starting text of my post but is a URL for an image (i’d upload a screenshot but you don’t allow that here).

However, the body of MailPoet allows for me to share the post excerpt. I’d like this to be the preview text, so the preview text, well, matches the text that it’s trying to preview 🙃. However, I do not see this option in your shortcodes list: https://kb.mailpoet.com/article/215-personalize-newsletter-with-shortcodes#list

Can this be added?