USENET is not a physical network, but rather a logical
network resting on top of several existing physical
networks. These networks include, but are not limited to,
UUCP, the ARPANET, an Ethernet, the BLICN network, an NSC
Hyperchannel, and a Berknet. What is important is that
two neighboring systems on USENET have some method to get
a new article, in the format listed here, from one system
to the other, and once on the receiving system, processed
by the netnews software on that system. (On UNIX systems,
this usually means the "rnews" program being run with
the article on the standard input.)
It is not a requirement that USENET sites have mail
systems capable of understanding the ARPA Internet mail
syntax, but it is strongly recommended. Since From,
Reply-To, and Sender lines use the Internet syntax,
replies will be difficult or impossible without an
internet mailer. A site without an internet mailer can
attempt to use the Path header line for replies, but this
field is not guaranteed to be a working path for replies.
In any event, any site generating or forwarding news
messages must have an internet address that allows them to
receive mail from sites with internet mailers, and they
must include their internet address on their From line.
