Raymond Tomlinson, the computer programmer who in 1971 invented email as it is known today and in the process transformed the “at” sign — @ — from a sparely used price symbol to a permanent fixture in the lives of millions of computer users around the world, died on Saturday at his home in Lincoln, Mass. He was 74.

His daughter Brooke Tomlinson McKenzie confirmed the death but said that the cause had not been determined.

In the late 1960s and early 1970s Mr. Tomlinson was working at a research and development company, Bolt, Beranek and Newman, on projects for the Arpanet, a forerunner of the Internet that was created for the Defense Department. At the time, the company had developed a messaging program, Sndmsg, that allowed multiple users of a time-share computer to send messages to one another. But it was a closed system, limited to users of a single computer.