[venusenvy47]

I just learned about the list-unsubscribe header in this article. Is this what allows Gmail to provide its own "Unsubscribe" button on certain emails next to the Subject line?? I've seen this button on certain emails and never knew how they decide when to implement it, or what it does.

[kirb]

That’s indeed what it is. It sends an automatic email to the List-Unsubscribe address, which if implemented correctly per the spec/regulations, authorises an immediate unsubscribe. More secure too because your email address is confirmed by SPF/DKIM. Nobody else with a copy of the email can unsubscribe you via List-Unsubscribe, like how just anyone can click the unsubscribe footer link if you forward it.