E-mail 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 e-mails 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 e-mails with the purpose of acquiring new customers or convincing old customers to buy something immediately.

Adding advertisements in e-mails sent by other companies to their customers.

Researchers estimate that as of 2004 the Email Marketing industry's revenues has surpassed the $1 billion/yr mark.