List-unsubscribe in Gmail

Whenever I receive other newsletters in Gmail I see a “unsubscribe” link right after the sender’s email header. e.g.

Cineplex <[email protected]> Unsubscribe
to me

However, the newsletters sent out with the Newsletter plugin don’t have the simple “unsubscribe” link on top in Gmail. Why is that?

It would be great to have it so that people don’t have to look into the body of newsletter to find the unsubscribe link.

Thanks.