Electronic mail, known as e-mail, is one of the most useful features of the internet. E-mail is a way of electronically sending messages to anyone in the world that has an e-mail address. Although e-mail isn't instantaneous, it is very quick. Sometimes it might only take a matter of seconds for an e-mail message to be received. When you compare this to mail delivered by the U.S. Postal Service (even next day service) you can understand why people who have been using e-mail for years refer to traditional letters as "snail mail."