An area that has recently attracted increasing attention is providing feedback on learners’ writing accuracy through the Internet. However, research in this area has largely focused on synchronous communication, i.e., chatting, with fewer studies assessing asynchronous technologies, i.e., e-mailing. Therefore, this study investigates the effectiveness of asynchronous computer-mediated corrective feedback-explicit and implicit, on increasing the correct use of prepositions. Forty-five Iranian elementary EFL learners at the ILI in Tehran were randomly assigned to two experimental groups, receiving explicit and implicit corrective feedback respectively, and one control group receiving no corrective feedback. Each group included 15 participants. After the treatment, a post-test was administered to assess the probable increase in the correct use of prepositions for the experimental groups compared to the control group. Analysis of the results through a one-way ANOVA revealed that the experimental group 1 who received explicit corrective feedback significantly outperformed the experimental group 2 and the control group. The experimental group 2 who received implicit corrective feedback showed no significant improvement over the experimental group 1 and the control group. Computer-mediated communication, asynchronous CMC, synchronous CMC, the Internet, corrective feedback, e-mail, chat. Although the findings support the current view on feedback through technology, due to the scarcity of research, more investigation is merited as there is much to gain regarding this burgeoning field.