.uucp
See UUCP for a fuller discussion of Unix-to-Unix Copy Protocol.
The name uucp was a pseudo-domain-style suffix used in the 1980s when identifying a hostname not connected directly to the Internet, but possibly reachable through other inter-network gateways. The suffix was appended to a UUCP bang path separated with a dot, e.g., host1!host2!host3.uucp.
The suffix prevented messages from being routed via the Simple Mail Transfer Protocol in mail exchangers, and it indicated that the hostname preceding it was reachable by UUCP networking. It was not a top-level domain in the Domain Name System root.
As UUCP hosts were not always uniquely named, and there was no official global table listing them, although the UUCP Mapping Project was an informal effort to create such a list, actual access to one required the use of a full bang path, which did not follow domain-name-style syntax, unless the particular software being used had been programmed to recognize particular hostnames in a domain style and route to them.
