TCP/IP Electronic Mail System Overview and History
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The History of TCP/IP Electronic Mail
Like some other file and message transfer protocols, e-mail on TCP/IP actually goes back to before TCP/IP and the Internet formally existed. The first protocols for e-mail were developed during the days of the ARPAnet. Prior to the creation of e-mail, several Internet RFCs, such as RFC 95 (yes 95, two digits, we are going back a long way here!) and RFC 155 describe physical mailing lists that were used for distributing documents in the early 1970s. It was this need to send documents that likely made TCP/IP pioneers realize how useful an electronic messaging system would be using the technology they were themselves creating.
The first Internet document describing electronic mail was probably RFC 196, published in 1971. It describes something called A Mail Box Protocol, a very rudimentary message transfer method using the predecessors of TCP/IP. This protocol was designed for the specific purpose of sending documents for remote printing. In those days it was not as common for people to use computers at interactive terminals as it is today, but the idea of electronically mailing documents was the same. The Mail Box Protocol was revised several times in 1971.
In the mid-1970s, work began to develop a more comprehensive method of implementing electronic mail on the fledgling Internet. The technique was originally described using a number of then-existing application-layer transfer protocols, including the File Transfer Protocol (FTP). In 1980 the Mail Transfer Protocol (MTP) was published in RFC 772. This was the first precursor of today's TCP/IP e-mail, and was defined using principles from the Telnet remote access protocol as well as FTP.
During the time that e-mail protocols were being developed in the 1970s, mail was being exchanged between host systems using a variety of different techniques. One of the most common used the Unix-to-Unix Copy Protocol (UUCP), which was designed to allow files to be transferred between UNIX systems, moving them from one connected system to the next. UUCP was also used for communicating Usenet newsgroup articles and other files.
In 1981, the modern TCP/IP electronic mail era came into being with the definition of the Simple Mail Transfer Protocol (SMTP). SMTP described in detail how mail could be moved directly or indirectly from one TCP/IP host to another without the need to use FTP or another file transfer method. It has its own detailed history and discussion in this Guide. Other complementary specifications were created at around the same time, which formalized or defined other components and elements of the system. We'll explore these pieces of the puzzle in the next two topics.
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