E-Mail Notifications: Making Unsubscription Easy
http://www.bohmann.dk/articles/making_unsubscription_easy.html

Bohmann, Kristoffer
Bohmann Usability
2001

Abstract:

Unsubscribing email newsletters and other email notification services can be an unpleasant and time-consuming experience. Most unsubscribe problems can be avoided by making the subscribers email visible and linking to an unsubscribe page in all emails.