Email marketing is a form of direct marketing which uses electronic mail as a means of communicating commercial or fund-raising 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 email messages with the purpose of enhancing the relationship of a merchant with its current or previous customers, to encourage customer loyalty and repeat business,
sending email messages with the purpose of acquiring new customers or convincing current customers to purchase something immediately,
adding advertisements to email messages sent by other companies to their customers, and
sending email messages over the Internet, as email did and does exist outside the Internet (e.g., network email and FIDO).
Researchers estimate that United States firms alone spent US $400 million on email marketing in 2006