Outlook has this functionality. I don't know if it's using the unsubscribe link scrape method, or the List-Unsubscribe header method. What it does is show an U

Outlook has this functionality. I don't know if it's using the unsubscribe link scrape method, or the List-Unsubscribe header method. What it does is show an Unsubscribe button above the email, which loads the unsubscribe URL into a small web panel below it.