Electronic mail (Russian: электронная почта), most commonly abbreviated email or e-mail, is a method of exchanging digital messages. Email systems are based on a store-and-forward model in which email server computer systems accept, forward, deliver and store messages on behalf of users, who only need to connect to the email infrastructure, typically an email server, with a network-enabled device for the duration of message submission or retrieval. Originally, email 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 email address (Russian: адрес электронной почты) 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, which were standardized in with RFC 2045 through RFC 2049, collectively called, Multipurpose Internet Mail Extensions (MIME).
An address such as “firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com” is used to demonstrate the sign-up process on a website, it indicates to the user they should fill in an actual email address at which they receive mail. “example.com and test.ru” is used in a generic and vendor-neutral manner. Example domains were created specifically for use in examples, so that people with real email accounts that happen to coincide with your examples don’t suffer the fallout of an unfortunate choice of example. They are not available for registration (Russian: регистрация) or transfer.
The foundation for today's global Internet email service was created in the early ARPANET and standards for encoding of messages were proposed as early as 1973 (RFC 561). An email 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 email was initially exchanged on the ARPANET in extensions to the File Transfer Protocol (FTP), but is today carried by the Simple Mail Transfer Protocol (SMTP), first published as Internet standard 10 (RFC 821) in 1982. In the process of transporting email messages between systems, SMTP communicates delivery parameters using a message envelope separately from the message (header and body) itself.
Messages are exchanged between hosts using the SMTP with software programs called mail transfer agents (MTA). Users can retrieve their messages from servers using standard protocols such as POP or IMAP, or, as is more likely in a large corporate environment, with a proprietary protocol specific to Lotus Notes or Microsoft Exchange Servers. Webmail interfaces allow users to access their mail with any standard web browser, from any computer, rather than relying on an email client (for example http://www.email.ru, http://www.email.com). Webmail solutions allow you to check your email (Russian: проверить почту) from anywhere in the world with internet access. Mail can be stored on the client, on the server side, or in both places. Standard formats for mailboxes include Maildir and mbox. Several prominent email clients use their own proprietary format and require conversion software to transfer email between them. Accepting a message obliges an MTA to deliver it, and when a message cannot be delivered, that MTA must send a bounce message back to the sender, indicating the problem.