The use of automated feedback (AF) has been increasing in English writing courses for emergency remote education (ERE) due to the escalating COVID-19 pandemic crisis in Vietnam. The ERE English writing courses for in-service bachelor programs demanded an effective, fast, free, and user-friendly AF tool that does not require a login ID, which can help students to develop English writing skills and increase their motivation and self-learning ability. The main objectives of Vietnamese in-service students were to improve their English writing skills and update teaching methodologies that integrate technology. Although many studies emphasized the impact of AF tools in normal teaching contexts, relatively less research was conducted the use of AF tools among in-service students. This study examined the contribution of the Marking Mate AF to the improvement of the English writing skills of in-service learners in ERE writing classes. The participants were 82 in-service students in a Vietnamese public university. The dataset included English writing pre and posttest results collected during the first semester of academic year 2020-2021. The mean scores (standard deviation) of these tests were used to benchmark the writing performance of students. A self-report survey was also conducted to investigate the attitude of students toward Marking Mate AF. The results demonstrated that the posttest score (8.739; SD = 0.8495) was higher than the pretest score (7.439; SD = 0.976). Students expressed favorable opinions toward the usefulness of Marking Mate. Based on the findings, the study discussed the pedagogical implications regarding the incorporation of AF in face-to-face and online classes.