The propagation of Usenet articles is indeed a defining function of the Network News Transfer Protocol (NNTP)—would I lie to you? J However, one critical area where NNTP differs from its progenitor, SMTP, is that NNTP is used not just for inter-server communication. It is also the protocol utilized for the initial posting of Usenet messages, and reading them as well. In fact, the majority of NNTP commands deal with the interaction between user client machines and NNTP servers, not communication between servers.

An NNTP client is any software program that knows the NNTP protocol and is designed to provide user access to Usenet. NNTP clients are usually called newsreaders, and provide two main capabilities to a user: posting (creating) and reading Usenet messages. Usenet newsreaders exist for virtually all hardware and software platforms, and range greatly in terms of capabilities, user interface and other characteristics. Most people today use a Usenet newsreader on a client computer that must make NNTP connections to a separate NNTP server to read and post news. These programs are analogous to e-mail clients, and in fact, many e-mail clients also function as NNTP clients.

Posting a Usenet message is the first step in the overall Usenet communication process (although many Usenet articles are actually replies to other articles, so it's a bit of a “chicken and egg” thing.) Article posting is quite straight-forward with NNTP. The client establishes a connection to the server and issues the POST command. If the server is willing to accept new articles it replies with a prompt for the client to send it the article. The article is then transmitted by the client to the server. Some newsreaders may “batch” new articles so they can be sent in a single NNTP session rather than submitting them one at a time.