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 (Source: Wikipedia).
In fact, Email marketing is the 1st generation digital marketing. It is an evolution of our traditional marketing, where we used to receive our newsletters and other communications through postal service.
In email marketing, internet acts as a means of communication transfer. We all have our email credentials during this smart phone era, to configure our android phone.