electronic mail or e-mail, the electronic transmission of messages, letters, and documents. In its broadest sense electronic mail includes point-to-point services such as telegraph and facsimile (fax) systems. It is commonly thought of, however, in terms of computer-based message systems where the electronic text file that is received can be edited, replied to, excerpted, or even pasted into another electronic document that can be used or manipulated by a word processor, desktop publishing system, or other computer program. Users of such systems, called store-and-forward or mailbox systems, can broadcast messages to multiple recipients, read and discard messages, file and retrieve messages, or forward messages to other users. Extensions to e-mail allow the user to add graphics and sound to messages, and files can be attached to e-mails. Computer-based messaging can take place on a single computer, a computer network, or across gateways linking different computer networks (as through the Internet). With the increasing use of e-mail, unsolicited commercial e-mail, known as spam, has become a significant problem. E-mail, especially through attachments, has also become a means for disseminating computer viruses and other malicious programs.