1. Introduction

   This document specifies the Network News Transfer Protocol (NNTP),
   which is used for the distribution, inquiry, retrieval, and posting
   of Netnews articles using a reliable stream-based mechanism.  For
   news-reading clients, NNTP enables retrieval of news articles that

   are stored in a central database, giving subscribers the ability to
   select only those articles they wish to read.

   The Netnews model provides for indexing, cross-referencing, and
   expiration of aged messages.  NNTP is designed for efficient
   transmission of Netnews articles over a reliable full duplex
   communication channel.

   Although the protocol specification in this document is largely
   compatible with the version specified in RFC 977(-> 3977prop) [RFC977], a number
   of changes are summarised in Appendix D.  In particular:

   o  the default character set is changed from US-ASCII [ANSI1986] to
      UTF-8 [RFC3629] (note that US-ASCII is a subset of UTF-8);

   o  a number of commands that were optional in RFC 977(-> 3977prop) or that have
      been taken from RFC 2980 [RFC2980] are now mandatory; and

   o  a CAPABILITIES command has been added to allow clients to
      determine what functionality is available from a server.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   An implementation is not compliant if it fails to satisfy one or more
   of the MUST requirements for this protocol.  An implementation that
   satisfies all the MUST and all the SHOULD requirements for its
   protocols is said to be "unconditionally compliant"; one that
   satisfies all the MUST requirements but not all the SHOULD
   requirements for NNTP is said to be "conditionally compliant".

   For the remainder of this document, the terms "client" and "client
   host" refer to a host making use of the NNTP service, while the terms
   "server" and "server host" refer to a host that offers the NNTP
   service.

1.1. Author's Note

   This document is written in XML using an NNTP-specific DTD.  Custom
   software is used to convert this to RFC 2629 [RFC2629] format, and
   then the public "xml2rfc" package to further reduce this to text,
   nroff source, and HTML.

   No perl was used in producing this document.