Electronic mail , most commonly abbreviated email or e-mail, is a method of exchanging al messages. E-mail systems are based on a model in which e-mail systems accept, forward, deliver and store messages on behalf of users, who only need to connect to the e-mail infrastructure, typically an, with a network-enabled device for the duration of message submission or retrieval. Originally, e-mail was always transmitted directly from one user's device to another's; nowadays this is rarely the case. |
|
| An electronic mail message consists of two components, the message header, and the message body, which is the email's content. The message header contains control information, including, minimally, an originator's and one or more recipient addresses. Usually additional information is added, such as a subject header field. |
| |
| Originally a text-only communications medium, email was extended to carry multi-media content attachments collectively called, (MIME). |
| |
| The foundation for today's global Internet e-mail service was created in the early and standards for encoding of messages were proposed as early as 1973. An e-mail sent in the early 1970s looked very similar to one sent on the Internet today. Conversion from the ARPANET to the Internet in the early 1980s produced the core of the current service. |
| |
| Network-based e-mail was initially exchanged on the ARPANET in extensions to thel(FTP), but is today carried by the SMTP), first published as in 1982. In the process of transporting e-mail messages between systems, SMTP communicates delivery parameters using a message envelope separately from the message (header and body) itself. |
| |
| Message format |
| |
| The Internet e-mail messages consist of two major sections: |
| |
- Header — structured into fields such as summary, sender, receiver, and other information about the e-mail.
- Body — the message itself as unstructured text; sometimes containing a signature block at the end. This is exactly the same as the body of a regular letter.
|
| The header is separated from the body by a blank line. |
| |
Each message has exactly oner, which is structured into. Each field has a name and a value. |
| Informally, each line of text in the header that begins with ar begins a separate field. The field name starts in the first character of the line and ends before the separator character ":". The separator is then followed by the field value (the "body" of the field). The value is continued onto subsequent lines if those lines have a space or tab as their first character. Field names and values are restricted to 7-bitI characters. Non-ASCII values may be represented using MIME encoded words. |
|
