UUCP

Details of this protocol are provided in RFC 976, RFC-976. UUCP is an old protocol. It was very heavily used when UNIX systems communicated only over RS232 serial lines, usually over modems. UUCP is implemented as a suite of programs developed back in the early 70's to provide this communications link. All that UUCP does is transfer files from one system to another. There is an additional mechanism where one system can direct the destination system to run a file through a specific program. Electronic mail in UUCP is simply requesting the destination machine to run "mail" on a data file.

UUCP communicates by means of "protocols", the most common being "g", a method for transmission of data over telephone lines and ensuring that the data is not corrupted. There are several other protocols, none universally available, and most oriented towards communication media other than telephone voice lines (such as dialup X.25, PAD X.25, or LAN connects).

UUCP operates over fixed system-to-system links, so sending mail from one system to another often has to traverse other intermediate systems.

The UUCP network is that set of machines that talk with each other via UUCP. Sending mail through this network requires that the sender know the network topology of UUCP links and specify a path from one machine to the next. The UUCP Mapping Project hides much of this complexity.