L2 learners’ email requests to authority figures generally contain pragmatic infelicities, requiring corrective feedback to enhance L2 learners’ knowledge of email pragmatics. This study investigated the effectiveness of reformulation, a feedback strategy for writing, for L2 learners of different proficiency levels in an eight-stage collaborative email writing task: (1) composing (pre-test), (2) reformulation and a native speaker model, (3) training, (4) noticing, (5) stimulated recall (reinforcement of noticing), (6) rewriting (the immediate post-test), (7) delayed post-test, and (8) interview. The participants were four pairs of EFL learners, two with high and two with low proficiency in English. The analysis of data included (1) learners’ pair talks, (2) the number of changes noticed and unnoticed by the learners in the reformulations and the native speaker model, (3) the number of revisions matching the reformulations and the native speaker model on the immediate and delayed post-tests, and (4) learners’ responses to interviews. The results suggest that reformulation is effective for L2 learners of different proficiency levels, and the enhanced email competence was sustained for at least four weeks. The learners’ positive perceptions of reformulation also support its effectiveness. In addition, pedagogical implications are provided for language teachers for the implementation of this feedback approach.