(Wiki) Email marketing is a form of direct marketing which uses electronic mail as a means of communicating commercial or fundraising messages to an audience. In its broadest sense, every email sent to a potential or current customer could be considered email marketing. However, the term is usually used to refer to:

• Sending emails with the purpose of enhancing the relationship of a merchant with its current or old customers and to encourage customer loyalty and repeat business.
• Sending emails with the purpose of acquiring new customers or convincing old customers to buy something immediately.
• Adding advertisements in emails sent by other companies to their customers.
• Emails that are being sent on the Internet (Email did and does exist outside the Internet, Network Email, FIDO etc.)