Email in one form or another existed from the early days of timesharing computers. Modern email was developed for the ARPANET. As the ARPANET started gaining popularity, it became obvious that it had several advantages over normal mail. There was an informality inherent in the messaging system which automatically inculcated a speedier response. It had an advantage over telephone in that one could come to the point directly without any obligatory small talk, moreover, records could be maintained and the sender and receiver did not have to be available at the same time.

In the early 1960's, with the development of timesharing computers that could run more than one process at once, many research organizations wrote programs to support the exchange of text messages and even real-time chat among users at different terminals. However, these systems were limited to use by a group of people using the same computer. In 1971, Ray Tomlinson developed the first email application for the ARPANET, consisting of a program called SNDMSG for sending mail, and a program called READMAIL for reading mail. These first email programs had simple functionality and were command line driven, but established the basic model still used today.

Lawrence Roberts, director of the IPTO, and Steve Crocker, then a program manager at IPTO, had READMAIL improved, and the new version was called RD which included additional functionalities like the ability to index email headers by subject and date, allowing users to format their Inbox and read and download messages in the order they wished.