A model is proposed for ISP customers to accept e-mail marketing in exchange for a discount on the Internet fee. Adherence to the model appeared to vary with age, number of e-mails received per day, and with the amount of the current fee. Authors recommend marketers send fewer, better-targeted, and personalized e-mails.
Micu, Anca et al. "An Economic Model of Permission Marketing: Win-win-win Relationship Building Among Marketers, ISPs, and Internet Users." AMA Winter Educators' Conference Proceedings 15 (2004): 86-94.