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Simple Mail Transfer Protocol (SMTP) – 1981 AD

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Simple Mail Transfer Protocol

Jonathan B. Postel (1943–1998), Eric Allman (b. 1955)

Email was the internet’s first “killer app.” From its very early days, the ability to exchange email with other scientists, professionals, and funding agencies was one of the key reasons that universities and businesses vied for a network connection. In the early years, there were stories of people turning down jobs or graduate school appointments to avoid losing access to network email.

Because email preceded the internet, network compatibility problems for sending messages emerged when it finally did come along. Different systems used different character sets (ASCII versus EBCDIC, for example) and even different word lengths (8 versus 12 bits). Some systems allowed special characters in usernames that other systems couldn’t even display. Getting these systems to communicate and exchange email in a reliable, repeatable manner was a major undertaking, with many protocols developed, fielded, and then replaced.

As its name implies, the Simple Mail Transfer Protocol (SMTP) was a simplified version of the more complex Mail Transfer Protocol. Invented by Jonathan Postel, one of the architects of the internet, the simplification involved breaking the act of sending a message from one computer to another into the explicit steps of establishing a connection, specifying where the message was coming from, individually specifying each of the message recipients, and finally sending the message. The protocol’s simplicity made programs easier to develop and debug.

Soon after SMTP was published, Eric Allman at the University of California, Berkeley, added SMTP support to a program he had written for delivering email called sendmail. Berkeley included sendmail along with support for the TCP/IP networking protocol in its UNIX operating system, making it possible for universities and businesses with internet connections to send and receive internet email using the SMTP standard.

SMTP has proven to be a remarkably durable standard. Although it has been updated several times, mail can still be sent and received using the basic protocol that was developed nearly four decades ago. This durability has come at a price, however. SMTP has no protections against receiving unwanted email, which led directly to the rise of spam.

SEE ALSO @Mail (1971), First Internet Spam Message (1978)

Computers on the internet exchange mail using the Simple Mail Transfer Protocol (SMTP).

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