Email marketing is the dinosaur of digital marketing and has been around since the beginning, while other platforms and tools come and go.
Over the past decade, email marketing has been improved and turned into the ultimate platform for permission based marketing. If your content is good and over time, your customers, clients and readers trust you and welcome your regular email.
Have a look at this infographic and see a why email marketing is such a good marketing tool:
Source: Digital Aptitude, Rory Kaluza