E-mail 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 e-mail sent to a potential or current customer could be considered e-mail 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 previous customers and to encourage customer loyalty and repeat business,
* sending e-mails with the purpose of acquiring new customers or convincing current customers to purchase something immediately,
* adding advertisements to e-mails sent by other companies to their customers, and
* sending e-mails over the Internet, as e-mail did and does exist outside the Internet (e.g., network e-mail and FIDO).


Many companies use e-mail marketing to communicate with existing customers, but many other companies send unsolicited bulk e-mail, also known as spam.

E-mail messages are easy to track. An advertiser can track users via autoresponders, web bugs, bounce messages, unsubscribe requests, read receipts, click-throughs, etc. These mechanisms can be used to measure open rates, positive or negative responses, and to correlate sales with marketing.