The rising of digital media has transformed the interactions between consumers and companies. Users' expectations have reached new heights fueled by the growth of ecommerce and smartphone penetration. In a context in which bidirectionality and personalized experiences are the new normal, email marketing is perceived by advertisers as an effective and highly profitable communication channel.Initially designed as an extension of post-based direct marketing programs, email marketing has become a key component of any advertising campaign due to its flexibility, the growing numbers of email users and the negligible cost per email sent. Moreover, recent research has proven the channel's significant contribution to overall sales. Hence, there is a growing interest from both scientist and advertisers on answering the question "What factors influence email marketing effectiveness?".The answer is relatively complex because of two major difficulties. First, it is unclear what is the best method to measure effectiveness. Second, it is required to consider a great number of intrinsic and extrinsic variables in order to determine their absolute and relative importance. Even though previous research has focused on particular stages or influence factors, the goal of this work is to adopt a holistic approach in order to obtain a unified theoretical predictive model for email marketing effectiveness.Considering this, the research has been structured in five stages: introduction to the topic, theoretical framework, research design, analysis and conclusions. These stages have been developed throughout nine chapters: the first one is covered in chapter 1, the second one in chapters 2 to 4, the third one in chapters 5 and 6, the fourth one in chapter 7 and the last one in chapter 8. Chapter 9 gathers the bibliography used through the research.Chapter 1 presents a brief introduction to the email marketing environment, followed by the statement of the research problem, articulated through a set of primary and secondary objectives. Then, the influencing factors and current approaches to the analysis of effectiveness are presented, hierarchy of effects and cultural dimensions models are succinctly described, and the relevance of the research is justified.Chapter 2 deepens on email marketing through an exhaustive literature review. First, different methodologies to measure effectiveness are described and a new unifying multi-staged definition is suggested. In addition, all influencing factors identified to date are listed, followed by the proposal of a taxonomy to articulate them.