In addition the use of the List-Unsubscribe mail header should be sent - see RFC2369.
I know it exists currently and links to “my preferences” but it should be updated, additionally this has some additional desirable effects in both Outlook.com and Gmail properties.
If this is available Gmail adds an additional “Unsubscribe” link in most cases (uses Google-foo to decide when to display it):
Original Google post announcing this feature:
https://plus.google.com/+Gmail/posts/euJxGkND1Ao
Unsubscribe can also be found on Gmail on mobile:
According to this article, using a “mailto” link for List-Unsubscribe is preferable to a HTTP link - it’s worth a read: