This article reports an eight-month investigation into the long-term impact of explicit instruction on the learnability of different aspects of email requests by a group of Vietnamese university students. Two intact classes were randomly assigned to the treatment (N = 13) and control conditions (N = 19). Over a four-week period, the treatment group received six hours of instruction which comprised consciousness-raising, meta-pragmatic explanation, repeated output practice and teacher feedback. The control group, on the other hand, only followed the usual syllabus. Results of the study indicate that the treatment group obtained significantly greater pre-to-posttest gains than the control group, and that their improvement was retained by the time of the eight-month delayed post-test. Despite the learners’ overall progress, however, it was also found that different aspects of their performance appeared to respond differently to instruction. The article supports the need for instruction of email politeness and discusses implications for future pedagogy and research. Keywords: email requests, e-politeness, learnability, second language, pragmatic instruction