This document discusses strategies for publishers to increase revenue through content walls, registration, and newsletters. It outlines different types of content walls like hard walls, metered walls, and hybrid premium models. An adaptive metered wall is proposed that uses machine learning to determine how many free articles a user gets before being asked to subscribe to a newsletter. The document also discusses using email as a way to develop audiences at scale and drive subscription conversions since email allows long-term marketing and monetization. It provides examples of clients growing their email lists and subscriptions significantly through PostUp's technology and strategies. In summary, the document proposes using content walls and email marketing to maximize audience growth and monetization for publishers.