As written about in the following link, email campaigners get better delivery and less spam listing if they don’t send confirmation emails after a subscriber unsubscribes. See the following article.
Why can’t such a feature work in phplist? All of the methods suggested in forums either do not work, or in the process of working, remove the sending of other important administrative emails.
Excerpt form the tech note:
“. . . over time it will affect your reputation and deliverability.”
Read all about it here: