How to Modify Post Excerpt Length

When adding posts to a newsletter and opting to show its excerpt, MailPoet limits the length of the excerpt to 60 words. If you wish to override the default value (e.g., display 20 words), you can use the following code:

add_filter('mailpoet_newsletter_post_excerpt_length', function() {
  return 20; /** # of words to display */

Just add this code to the bottom of your functions.php file inside your current theme folder.