An E-mail is a service used for sending digital messages via Internet. It uses a protocol for the transfer of messages from sender to receiver which is called as SMTP (Simple mail transfer protocol). The transmission takes place across IP (Internet protocol). Earlier e-mail systems required that both sender and receiver must be online at the same time for transmission of messages and now it is based on store and forward technique which defines that e-mail servers will accept, deliver, forward and store messages of the sender. Neither sender nor the receiver has to be online at the same time.