What is E-mail marketing?

Source -wikipedia
Email marketing is directly marketing a commercial message to a group of people using email. In its broadest sense, every email sent to a potential or current customer could be considered email marketing. It usually involves using email to send ads, request business, or solicit sales or donations, and is meant to build loyalty, trust, or brand awareness. Email marketing can be done to either sold lists or current customer database. Broadly, 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.

Researchers estimate that United States firms alone spent US $1.51 billion on email marketing in 2011 and will grow to $2.468 billion by 2016.