ABSTRACT Though e-mail has become a common interpersonal communication medium, it does not mean that this medium is used without difficulty. While people can write e-mails to peers in any manner they like, writing e-mails to authority figures requires higher pragmatic competence and critical language awareness of how discourse shapes and reflects power asymmetry in an institutional context. For L2 learners, the challenge of composing this type of e-mail can be greater due not only to their limited linguistic ability but also their unfamiliarity with the target culture's norms and values. To provide a deeper understanding of how an L2 learner develops email literacy in the target language environment, this paper presents a longitudinal case study of a Taiwanese graduate student's e-mail practice in English during her studies at a U.S. university for two and a half years. Using a critical discourse analysis approach, the study reveals the complexity of an L2 learner's evolving e-mail practice and struggle for appropriateness, particularly in her e-mail communication with professors. Her development of e-mail literacy is discussed in relation to her evolving understanding of the e-mail medium, changing performance of student identity, increasing knowledge of student-professor interaction and realization of culture-specific politeness.