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 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.

Researchers estimate that United States firms alone spent US$400 million on e-mail marketing in 2006.

Advantages

1. A mailing list provides the ability to distribute information to a wide range of specific, potential customers at a relatively low cost.
2. Compared to other media investments such as direct mail or printed newsletters, e-mail is less expensive.
3. An exact return on investment can be tracked ("track to basket") and has proven to be high when done properly. E-mail marketing is often reported as second only to search marketing as the most effective online marketing tactic.
4. The delivery time for an e-mail message is short (i.e., seconds or minutes) as compared to a mailed advertisement (i.e., one or more days).
5. An advertiser is able to "push" the message to its audience, as opposed to website-based advertising, which relies on a customer to visit that website.
6. 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.
7. Advertisers can generate repeat business affordably and automatically.
8. Advertisers can reach substantial numbers of e-mail subscribers who have opted in (i.e., consented) to receive e-mail communications on subjects of interest to them.
9. Over half of Internet users check or send e-mail on a typical day.
10. Specific types of interaction with messages can trigger (a) other messages to be delivered automatically, or (b) other events, such as updating the profile of the recipient to indicate a specific interest category.
11. E-mail marketing is paper-free (i.e., "green").
12. Tracking and response metrics enables tuning and optimisation of the E-mail marketing channel by a process of testing different variants and calculation of statistically significant results.
13. E-mail is popular with digital marketers, rising an estimated 15% in 2009 to £292m in the UK.