Nathaniel S. Borenstein (born September 23, 1957) is an American computer scientist. He is one of the original designers of the MIME protocol for formatting multimedia Internet electronic mail and sent the first e-mail attachment.
Borenstein received a B.A. in Mathematics and Religious Studies from Grinnell College in 1980, and a Ph.D in Computer Science from Carnegie Mellon University in 1985. Previously he attended Ohio State University (1974–75), Deep Springs College, California (1975–76), and the Hebrew University of Jerusalem, Israel (1978–79). While at CMU, he co-developed the email component of the Andrew Project. The Andrew Message System was the first multi-media electronic mail system to become used outside of a laboratory. In 1989 he became a member of technical staff at Bellcore (Bell Communications Research). There he developed a series of standards so the various electronic mail systems could exchange multimedia messages in a common way. He is responsible for sending the first email attachment on March 11, 1992.