Electronic mail systems are either computerized or noncomputerized. Importan

Electronic mail systems are either computerized or noncomputerized. Important among the computerized systems are the terminal-based ones organized into networks of various sizes. Most noncomputerized electronic mail systems such as facsimile units of various kinds are simple, turnkey systems that require little effort to install. Though often of value in conventional applications, these systems have only interim(间歇) worth in office automation unless they can be electronically integrated.
    Communication in an EMS is either synchronous or nonsynchronous. People involved in synchronous communication must be available at the same absolute time, such as during a telephone call. A nonsynchronous system frees its users from this time constraint; sender and recipient may be involved at different times.
    Electronic systems output soft copy or hard copy. Soft copy is preferred for its ease of manipulation and reduction in paper handling, but many applications will continue to require hard copy for some time to come.