Application software system originally developed for store-and-forward text messaging over a packet-based computer network. E-mail originated in the mid-1960s for communications between time-share computer users. E-mail quickly became popular for government and military communications in the late 1960s and early 1970s, especially as an application on the Advanced Research Projects Agency Network (ARPANET), which was the predecessor to the Internet. E-mail was popularized in the late 1970s and early 1980s, as part of the office automation concept designed to lead us toward the paperless office. E-mail relies on a client/server architecture can be implemented over local area networks (LANs) or wide area networks (WANs) such as the public Internet. Some e-mail systems, such as Microsoft Outlook, support not only plain text, but also rich text and Hypertext Markup Language (HTML) formatting. Unfortunately, communication with e-mail clients not supporting rich text or HTML creates considerable formatting incompatibilities. E-mail now permits the attachment of other forms of information, including binary files, images, graphics, and even digitized voice and video. E-mail system features typically include address book, confirmation, and formatting. See also address book, ARPANET, client/server, confirmation, e-mail address, format, HTML, IMAP, Internet, MIME, plain text, POP, rich text, SMTP, spam, store-and-forward, and time-sharing.