In the early 1970's, Ray Tomlinson was working on a small team developing the TENEX operating system, with local email programs called SNDMSG and READMAIL. In late 1971, Tomlinson developed the first ARPANET email application when he updated SNDMSG by adding a program called CPYNET capable of copying files over the network, and informed his colleagues by sending them an email using the new program with instructions on how to use it.
