Email marketing is a subdiscipline of online marketing, specifically of direct marketing, and refers to the act of sending digital messages for marketing purposes. These email messages inform customers and guests about offers, services, and news and can address individuals (one-to-one) as well as whole groups of persons (one-to-many). Newsletters are a classic example of email marketing. Email automation takes the matter further, addressing users at a specific time, for instance, on the user’s birthday or when new promotions or new products are available. It is crucial to determine the best frequency to send emails: While newsletters should be sent at regular intervals, email automation implies sending messages on an irregular basis. This form of direct communication between a company and its customers or guests is essential in modern customer care and an important means to increase customer loyalty, generate new customers, and maintain regular customer contact.