E-mail or electronic mail is a digital message that is sent through a computer network. The first electronic mail was sent to the then ARPANET in 1982 (RFC 561). In order to get e-mail, both the sender and the recipient had to be online in the early e-mail system. Current e-mails do not have this problem. E-mail servers receive and store mail and send it later. The user or recipient or computer does not need to be online, it only needs to have an active e-mail address on an e-mail server.
An e-mail message consists of three parts - the envelope of the message, the header of the message (where the message is and from whom the information is) and the message. The header carries mail control information that contains (at least) the sender's e-mail address, or the address of one or more recipients. But usually there is more detailed information such as a field for header content and message sending information, receiving information etc.
Originally text messaging (8-bit ASCII and others) was the medium of communication but e-mail can now also send multimedia and attach attachments. This is a process of sending RFC from 2045 to 2049. This RFC is called MIME which means Multipurpose Internet Mail Extension
Network-based e-mails in Orpanet were first exchanged with FTP (File Transfer Protocol), but are now exchanged with SMTP (Simple Mail Transfer Protocol), first published in 1982 (RFC 821). In the process of sending messages, SMTP stores different delivery information (from messages and headers) in its envelope or envelope.