Email

Message systems existed on time-sharing computers before networks—users could leave notes for each other on shared mainframes. But sending messages between different machines required something new. The ARPANET, connecting university and research computers, provided the network; what remained was creating the addressing and transmission conventions.

Ray Tomlinson at Bolt, Beranek and Newman (BBN) wrote the first network email program in late 1971. His crucial innovation was the '@' symbol to separate user names from machine names—a convention that became universal. SNDMSG and CPYNET, adapted from existing file transfer and local messaging programs, sent the first messages between computers on the ARPANET.

The adjacent possible required several elements to converge. Time-sharing systems already had local messaging capabilities. The ARPANET provided the network infrastructure. File transfer protocols (like FTP) demonstrated that data could move between machines. The insight was recognizing that personal messages could use these same mechanisms, creating a communication medium that was neither phone (synchronous) nor letter (slow).

Email adoption on the ARPANET was immediate and intense—by 1973, three-quarters of network traffic was email. The killer application for computer networking turned out to be human communication, not the remote computation originally envisioned. Standards evolved: headers, reply functions, mailing lists, and eventually SMTP (1982) formalized transmission protocols.

The transition to mass adoption came with the internet's commercialization in the 1990s. CompuServe, Prodigy, and AOL offered email to consumers. Hotmail (1996) pioneered free web-based email, acquired by Microsoft for $400 million. Yahoo Mail followed. Gmail (2004), offering unprecedented storage and search, raised expectations for what email could be.

Geographic factors reflected the ARPANET's structure. BBN in Cambridge, Massachusetts, built the network infrastructure. Stanford, UCLA, and MIT contributed users and development. The protocol's decentralized design reflected academic values—anyone could run a mail server, unlike later proprietary messaging systems.

The cascade effects were profound. Business communication shifted from memos and phone calls to email threads. Written records proliferated. Work expanded beyond office hours as email followed people home. Spam emerged as a tragedy of the commons. Phishing exploited trust in familiar formats. By the 2000s, email overload had become a recognized productivity problem.

By 2025, email remained essential—the universal digital address, required for virtually every online account—even as messaging apps, collaboration tools, and social media fragmented communications. The technology that first demonstrated the value of networked human communication had become invisible infrastructure, complained about constantly and utterly indispensable.