Email marketing is marketing a commercial message to a group of people using electronic mail. Database marketing has always been used on communication. There is no point in building and maintaining a database unless you use it to create personal communications to your customers, based on information in the database, and designed to increase loyalty, retention, referrals and cross sales.
Before the internet, such communications were rare. Personal letters were expensive, and retention building outbound phone calls were out of reach for most marketers. The web has changed everything. Now you can afford to do many interesting and profitable things that you never could do before. Email marketing has changed the way promotion of products.