E-mail is short for electronic mail, messages communicated via computer rather than paper. Although the term e-mail encompasses a variety of computer-to-computer transactions, it is most associated with communication via the Internet. The Internet is a vast computer network made up of many individual computers around the world. E-mail is the most-used Internet application, permitting people to exchange greetings and information with incredible speed. It is estimated that more than 15 billion e-mail messages are sent every year.
In the early 1960s computers were room-sized machines that were often shared by many people. These time-sharing computer systems featured individual terminals hooked up to the host computer. Users could leave messages for one another by storing them in a particular file on the computer or by using an internal mail delivery program. By the late 1960s the ARPAnet had been formed. This was a US Department of Defense project in which government and academic researchers collaborated to develop a wide-area network of computers. By 1971 the ARPAnet linked computers at 15 different locations across the United States.
Ray Tomlinson was an ARPAnet researcher affiliated with the company Bolt Beranek and Newman (now GTE) in Cambridge, Massachusetts. In 1971 he developed an electronic mail system for the ARPAnet from two existing programs. One was a time-sharing mail program called SENDMSG and the other was an experimental file transfer program called CPYNET. Tomlinson chose an address syntax of UserName@HostComputer, where the @ symbol (meaning "at"), indicated that an e-mail recipient was at a different location, i.e., using a different host computer. After testing the programs, he e-mailed his ARPAnet colleagues about the new feature and shared the software with them. Improvements came quickly, including an e-mail management system developed by Larry Roberts that allowed users to view a list of incoming messages and to forward, file, save and reply to specific messages. Within two years e-mail became the most widely used application developed for the ARPAnet.
By the early 1990s the ARPAnet had evolved into a public Internet. Personal computers were very popular, and companies called Internet service providers began providing dial-up access to the Internet and its vast resources, including the World Wide Web. Internet traffic (including e-mail) occurs via a client-server interaction. Servers are powerful computers that are in communication with each other throughout the network. They run programs that allow them to process requests from different clients. An e-mail client is software, usually residing on the user's computer, that allows the user to send and receive e-mail. Users must first establish an e-mail account with an Internet service provider or an online business offering such accounts.
In order for different e-mail clients and servers to communicate with each other, most e-mail is processed using common standards of communication called protocols. The protocol most widely used for incoming e-mail is called Post Office Protocol 3 (POP3). The protocol used for most outgoing e-mail is called Simple Mail Transfer Protocol (SMTP), which is a TCP/IP protocol. When a user tells their e-mail client they want to check e-mail, the client contacts its POP3 server, which requires a user name and password for identification, and allows the e-mail client access to any messages stored there. The POP server acts as an electronic post office, holding messages until they are requested. Some e-mail systems use the newer Internet Message Access Protocol (IMAP) in place of POP3. Although similar, IMAP includes additional features, such as the ability to store messages on the server and to search them using keywords.
E-mail messages are usually short text messages typed into the computer directly. In addition, computer documents and files generated in a variety of software programs can be "attached" to the e-mail message and sent along with it. Because most e-mail systems can only handle text files, binary files and formatted text files must be converted into ASCII text to be sent as e-mail attachments. Such files must be encoded by the sender and decoded by the receiver. Two encoding/decoding systems commonly used include Multipurpose Internet Mail Extensions (MIME) and UUENCODE/UUDECODE. However, the recipient can only open and view the attachment if they have the same software in which the attachment was originally created.
One very popular use of e-mail is for mailing lists. A mailing list is a single e-mail address that identifies a list of e-mail addresses. A user can send an e-mail to the mailing list name and that e-mail will be automatically forwarded to every address on the list. Although e-mail has revolutionized communications, it has not come without problems. Junk mail, a common problem with traditional "snail-mail" services, also occurs via e-mail and is called spam. Spam is generally considered to be unsolicited or annoying e-mail from commercial sources. A much more serious problem is caused by the e-mailing of computer viruses. These are often destructive computer programs that are sent as attachments to e-mails. Many can forward copies of themselves to all of the e-mail addresses on a recipient's computer, allowing them to spread widely and quickly.
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