UUCP stands for UNIX-to-UNIX Copy, a UNIX protocol and utility for copying (sending) files between two UNIX computers on a network. UUCP was originally intended for transferring files over an asynchronous serial transmission interface such as RS-232. With UUCP, you can transfer files via a direct cable connection between serial ports on two computers by using a null modem cable or over telephone lines by using modems connected to the serial ports of each computer. A version of UUCP has been developed for transferring files over Ethernet as well.
UUCP was also used for transferring electronic mail messages (e-mail) between hosts in the early days of the Internet. A UNIX host used UUCP to transfer mail to a remote host simply by executing the MAIL program on the remote UNIX host and having it run on the local message file to be delivered.
UUCP uses the well-known port number 117 for its path service and number 540 for the UUCP daemon called UUCPD. UUCP has been eclipsed by File Transfer Protocol (FTP) as a general protocol for moving files between hosts and by Simple Mail Transfer Protocol (SMTP) for transferring e-mail messages.
Third-party vendors have created UUCP gateway connectors for Microsoft Exchange Server to enable Exchange to send and receive UUCP mail over the Internet.