Thank you for understanding @anonymous20,
We fully get the issue. As far as we fill HTML in the email notification content, it was substring the content (the <a> tag was opened and closed on the wrong place) and somehow the support topic linked and unsubscribed liked were missed.
If the email content is not filled as HTML or ignores the substring function this kind of issue never takes place. So the content will be unlimited.
In the second case the following code should be used. So the limit will be ignored:
add_filter('wpforo_email_notification_post_body_length', function(){return 0;});