The increasing use of the Internet and social networks has caused many people to fear missing out, and this has prompted many marketers to start using FOMO appeals in their promotions. In the first half of the theoretical part of the paper, FOMO and FOMO in the promotion are defined, the link between psychology and FOMO is explained, techniques for using FOMO are presented, and the advantages of using FOMO in the promotion are highlighted. In the second half of the theoretical part of the paper, the concept of electronic mail is explained, an insight into the history of electronic mail is given, and the latest information related to electronic mail today is presented. Also, it is shown how mass communication is carried out by e-mail and the essential elements of e-mail, the most important e-mail metrics are explained, and the advantages of using e-mail are presented. This theoretical background made it possible to conduct research whose goal was to determine how and to what extent the use of FOMO appeals within emails is related to click-through, conversion, and unsubscribe rates. The research was conducted on a sample of 100 email campaigns. After analyzing the data, it was possible to conclude that using FOMO appeals within emails is associated with a higher click-through rate, conversion rate, and unsubscribe rate. Finally, recommendations for future research are given.