Email marketing is the act of sending a commercial message, typically to a group of people, using email. In its broadest sense, every email sent to a potential or current customer could be considered email marketing. It involves using email to send advertisements, request business, or solicit sales or donations. Email marketing strategies commonly seek to achieve one or more of three primary objectives, to build loyalty, trust, or brand awareness. The term usually refers to sending email messages with the purpose of enhancing a merchant's relationship with current or previous customers, encouraging customer loyalty and repeat business, acquiring new customers or convincing current customers to purchase something immediately, and sharing third-party ads. History Email marketing has evolved rapidly alongside the technological growth of the 21st century. Before this growth, when emails were novelties to most customers, email marketing was not as effective. In 1978, Gary Thuerk of Digital Equipment Corporation (DEC) sent out the first mass email to approximately 400 potential clients via the Advanced Research Projects Agency Network (ARPANET). He claims that this resulted in $13 million worth of sales in DEC products, and highlighted the potential of marketing through mass emails. However, as email marketing developed as an effective means of direct communication, in the 1990s, users increasingly began referring to it as "spam", and began blocking out content from emails with filters and blocking programs. To effectively communicate a message through email, marketers had to develop a way of pushing content through to the end user without being cut out by automatic filters and spam removing software. Historically, it has not been easy to measure the effectiveness of marketing campaigns because target markets cannot be adequately defined. Email marketing carries the benefit of allowing marketers to identify returns on investment and measure and improve efficiency. Email marketing allows marketers to see users' feedback in real-time and monitor how effective their campaign is in achieving market penetration, revealing a communication channel's scope. At the same time, however, it also means that the more personal nature of specific advertising methods, such as television advertisements, cannot be captured. Types Email marketing can be carried out through different types of emails: Transactional emails Transactional emails are usually triggered based on a customer's action with a company. To be qualified as transactional or relationship messages, these communications' primary purpose must be "to facilitate, complete, or confirm a commercial transaction that the