Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

Electronic mail (e-mail) is probably the most common application used on enterprise networks and the Internet. Some enterprise networks were built with e-mail in mind. Messaging has many obvious benefits. If a person isn't available to pick up a message immediately, the message is held in an e-mail box until it can be picked up. Files can be exchanged by attaching them to messages. Today, collaborative applications are built upon electronic messaging systems and messaging has become an important part of network applications.

Chat and instant messaging are forms of synchronous communications. Like a voice telephone call, a chat or instant messaging session is live and each user responds to the other in real time. In contrast, discussion forums and electronic mail are forms of asynchronous communications. Some amount of time may pass before a person responds to a message. In a discussion forum, a message sits in a message queue for other people to read and respond to at any time, or until the message falls out of the queue. These two forms of communication, which are accessible to any Internet user from just about any Internet-attached system, may be the most important aspect of the Internet. They promote a new form of instant global communication and collaboration. In the case of discussion forums and e-mail, the delay in communication is beneficial-it gives people time to think about and research their responses.

There are many different e-mail systems in use on networks, mainframe systems, and public networks. The Internet's message transport standard is SMTP (Simple Mail Transfer Protocol), which is supported by mail server protocols such as POP (Post Office Protocol) and IMAP (Internet Message Access Protocol). The growth of the Internet and intranets has promoted its acceptance almost everywhere. In addition, SMTP-compatible e-mail services are integrated into browsers. As a result, almost every Web user has an SMTP mail client available for their use.

Legacy mail systems include IBM PROFS (Professional Office System) and SNADS (SNA Distributed Services), which were used in the IBM mainframe environment, and VAXmail or All-In-1 in the DEC environment. A single organization might have numerous e-mail systems that were implemented in the days when departments or workgroups maintained their own LANs. As the organization was interconnected, e-mail gateway systems were often employed to translate messages among the different systems. The X.400 Message Handling System was supposed to provide a standard for exchanging messages among a wide variety of messaging platforms, but X.400 never caught on. Today, most network administrators prefer to use a single mail standard, and that has become the Internet messaging protocols. Vendors are also integrating the standard into their proprietary systems. Because of its pervasiveness, the Internet mail standard is covered in this section.

Still, three major messaging platforms are available that offer more than just electronic mail. Lotus Domino, Microsoft Exchange, and Novell GroupWise are enterprise collaboration and groupware platforms, as discussed later.