Email, short for electronic mail, is a method of sending digital messages between devices over a computer network. Most email travels across the Internet from one mail server to another, and people read it with an email program or a web browser.
History of Email
Creator: Ray Tomlinson. Year: 1971.
Time-sharing came in the early 1960s. It let users on the same computer send messages to each other. The Massachusetts Institute of Technology (MIT) built one such system in 1965. It ran on its CTSS computer. Most makers of mainframe and minicomputer systems built their own mail programs. These programs did not work with each other.
In 1971 the first network mail was sent on the ARPANET. The ARPANET was a research network. ARPA, a research agency of the United States Department of Defense, funded it. That first message introduced an address form. The form puts an at sign (@) between the user name and the system name. The form is still used today.
CompuServe, IBM and Xerox used in-house mail systems in the 1970s. Digital Equipment Corporation (DEC) released ALL-IN-1. It came out in 1982. Hewlett-Packard released HPMAIL in 1982. The Simple Mail Transfer Protocol (SMTP) was put into use on the ARPANET in 1983.
In the late 1980s and early 1990s, many people expected a commercial system or the X.400 standard to win. Commercial traffic was allowed on the Internet in 1995. After that date, Internet protocols became the standard for email. They were SMTP, Post Office Protocol version 3 (POP3) and Internet Message Access Protocol (IMAP).
Changelog and latest update
The Internet Message Format defines the header fields of an email. Examples are From, To, Subject and Date. It also defines the body that follows them. RFC 5322 was published in October 2008. Its text recommends no more than 78 characters per header line. It sets a limit of 998 characters per line. Fields with other character sets are encoded under RFC 2047.
SMTP is defined in RFC 5321. It was published in October 2008. It describes how a sending server opens a session. The server names the sender and recipient. It then transfers the message body. POP3 is defined in RFC 1939. It was published in May 1996. A POP3 client downloads messages from the server. It usually removes them there.
IMAP keeps messages on the server. An IMAP client can show the same folders, flags and search results. It works on a phone, a laptop and a web browser. RFC 9051 defines version 4rev2 of the protocol. Mail servers and mail programs use it to keep mail in sync between devices.
Latest update: IMAP4rev2, RFC 9051, 2021-08
The RFC Editor page for RFC 9051 is titled Internet Message Access Protocol (IMAP) - Version 4rev2. The page carries the date August 2021. It is the current IMAP standard listed on that page. Email programs that support it can read the same folders from several devices at once.
Usage examples
Email uses SMTP to send a message. It uses IMAP or POP3 to read it. Domain Name System (DNS) records tell other servers where to deliver mail. The examples below show an MX record. They show a mailto link in HTML. They show a Python program that sends a message. They show an SMTP session.
example.com. 3600 IN MX 10 mail.example.com.
example.com. 3600 IN MX 20 backup-mail.example.net.
mail.example.com. 3600 IN A 203.0.113.25MX stands for Mail Exchanger. These DNS records tell other mail servers which host accepts email for example.com. The lower number 10 is tried first. The backup host with number 20 gets mail only when the first host does not answer.
<p>
Request a quote from our sales desk:
<a href="mailto:sales@example.com?subject=Website%20quote">
sales@example.com
</a>
</p>HTML is the markup language of web pages. The mailto link opens the visitor's email program. It fills in the address and a subject line. The browser passes the address to the email program on the visitor's device.
import smtplib
from email.message import EmailMessage
msg = EmailMessage()
msg["From"] = "rod@example.com"
msg["To"] = "client@example.org"
msg["Subject"] = "Test message"
with smtplib.SMTP("mail.example.com", 587) as server:
server.starttls()
server.login("rod@example.com", "app-password-here")
server.send_message(msg)This program builds a message with the standard email package. It sends the message through an SMTP server on port 587. The starttls call encrypts the session before the login. The login uses an application password. The mail provider issues that password for programs.
220 mail.example.com ESMTP ready
EHLO client.example.org
250 mail.example.com
MAIL FROM:<rod@example.com>
250 2.1.0 OK
RCPT TO:<client@example.org>
250 2.1.5 OK
DATA
354 End data with <CRLF>.<CRLF>SMTP stands for Simple Mail Transfer Protocol. The client says hello with EHLO. It names the sender with MAIL FROM. It names the recipient with RCPT TO. The server answers each command with a three-digit code. The code 250 means the step succeeded.
References
These sources are outside Websnoogie and were checked on 2026-10-12.
Simple Mail Transfer Protocol (RFC 5321)
IETF, RFC Editor
The standard that defines SMTP, the protocol used to transfer email between servers and from mail programs to mail servers. It lists the commands, reply codes and session steps that a sending server follows. The page is the reference for the MAIL FROM and RCPT TO commands used in the session example.
Internet Message Format (RFC 5322)
IETF, RFC Editor
The standard that defines the format of an email message, including the header fields From, To, Subject and Date, the line length limits, and the body. It was published in October 2008. The page sets the rule that a message has one header block and one body, separated by a blank line.
Internet Message Access Protocol Version 4rev2 (RFC 9051)
IETF, RFC Editor
The current IMAP standard, which lets an email program read, search and manage mail that stays on a server. The RFC Editor page lists the date as August 2021.
Post Office Protocol Version 3 (RFC 1939)
IETF, RFC Editor
The standard for POP3, the older protocol that downloads mail from a server to one device. The page lists the publication date as May 1996 and describes how a client retrieves and deletes messages. It is the reference for the POP3 commands that a mail program sends to a server.
Email
Wikipedia
The encyclopedia article on electronic mail. It covers the store-and-forward model, the history of mail protocols, mail servers, webmail, and spam. The page covers the history of the protocols and mail servers.
Email on launch day: the DNS records come first
On launch day, a new website goes live, and email can stop working at the same moment. Email depends on DNS records that tell other servers where your messages belong. If a record is wrong or missing, messages bounce or land in spam. We check every mail record before we switch a site live, and we send one test message from start to finish. You should not learn about a broken mailbox from a customer who could not reach you.
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