If you wanted to do "retail" level transactions like sending an email, you needed to know the path, like systemA!systemB!destinationsystem!user Usenet systems

If you wanted to do "retail" level transactions like sending an email, you needed to know the path, like systemA!systemB!destinationsystem!user Usenet systems had established neighbors communicating with UUCP and used a flooding algorithm to get messages to the entire network of systems. All built on top of these point-to-point links, could be done over the Internet (NNTP) but it wasn't required. This was a big enough thing that specialized modems for UUCP were popular: https://en.wikipedia.org/wiki/Telebit https://en.wikipedia.org/wiki/Telebit