8.  Transmission Formats

   While this Draft does not specify transmission methods, except to
   place a few constraints on them, there are some data formats used
   only for transmission that are unique to news.

8.1.  Batches

   For efficient bulk transmission and processing of news articles, it
   is often desirable to transmit a number of them as a single block of
   data, i.e., a "batch".  The format of a batch is:

      batch         = 1*( batch-header article )
      batch-header  = "#! rnews " article-size eol
      article-size  = 1*digit

   A batch is a sequence of articles, each prefixed by a header line
   that includes its size.  The article size is a decimal count of the
   octets in the article, counting each EOL as one octet regardless of
   how it is actually represented.

      NOTE: A relayer might wish to accept either a single article or a
      batch as input.  Since "#" cannot appear in a header name,
      examination of the first octet of the input will reveal its
      nature.

      NOTE: In the header line, there is exactly one blank before
      "rnews", there is exactly one blank after "rnews", and the EOL
      immediately follows the article size.  Beware that some software
      inserts non-standard trash after the size.

      NOTE: Despite the similarity of this format to the executable-
      script format used by some operating systems, it is EXTREMELY
      unwise to just feed incoming batches to a command interpreter in
      the anticipation that it will run a command named "rnews" to
      process the batch.  Unless arrangements are made to very tightly
      restrict the range of commands that can be executed by this means,
      the security implications are disastrous.

8.2.  Encoded Batches

   When transmitting news, especially over communications links that are
   slow or are billed by the bit, it is often desirable to batch news
   and apply data compression to the batches.  Transmission links
   sending compressed batches SHOULD use out-of-band means of
   communication to specify the compression algorithm being used.  If
   there is no way to send out-of-band information along with a batch,
   the following encapsulation for a compressed batch MAY be used:

         ec-batch             = "#! " compression-keyword eol
                                compressed-batch
         compression-keyword  = "cunbatch"

   A line containing a keyword indicating the type of compression is
   followed by the compressed batch.  The only truly widespread
   compression keyword at present is "cunbatch", indicating compression
   using the widely distributed "compress" program.  Other compression
   keywords MAY be used by mutual agreement between the hosts involved.

      NOTE: An encapsulated compressed batch is NOT, in general, a text
      file, despite having an initial text line.  This combination of
      text and non-text data is often awkward to handle; for example,
      standard decompression programs cannot be used without first
      stripping off the initial line, and that in turn is painful to do
      because many text-handling tools that are superficially suited to
      the job do not cope well with non-text data, hence the
      recommendation that out-of-band communication be used instead when
      possible.

      NOTE: For UUCP transmission, where a batch is typically
      transmitted by invoking the remote command "rnews" with the batch
      as its input stream, a plausible out-of-band method for indicating
      a compression type would be to give a compression keyword in an
      option to "rnews", perhaps in the form:

      rnews -d decompressor

      where "decompressor" is the name of a decompression program (e.g.,
      "uncompress" for a batch compressed with "compress" or "gunzip"
      for a batch compressed with "gzip").  How this decompression
      program is located and invoked by the receiving relayer is
      implementation-specific.

      NOTE: See the notes in Section 8.1 on the inadvisability of
      feeding batches directly to command interpreters.

      NOTE: There is exactly one blank between "#!" and the compression
      keyword, and the EOL immediately follows the keyword.

8.3.  News within Mail

   It is often desirable to transmit news as mail, either for the
   convenience of a human recipient or because that is the only type of
   transmission available on a restrictive communication path.

   Given the similarity between the news format and the MAIL format, it
   is superficially attractive to just send the news article as a mail
   message.  This is typically a mistake: mail-handling software often
   feels free to manipulate various headers in undesirable ways (in some
   cases, such as Sender, such manipulation is actually mandatory), and
   mail transmission problems, etc. MUST be reported to the
   administrators responsible for the mail transmission rather than to
   the article's author.  In general, news sent as mail should be
   encapsulated to separate the MAIL headers and the news headers.

   When the intended recipient is a human, any convenient form of
   encapsulation may be used.  Recommended practice is to use MIME
   encapsulation with a content type of "message/news", given that news
   articles have additional semantics beyond what "message/rfc822"
   implies.

      NOTE: "message/news" was registered as a standard subtype by IANA
      22 June 1993.

   When mail is being used as a transmission path between two relayers,
   however, a standard method is desirable.  Currently the standard
   method is to send the mail to an address whose local part is "rnews",
   with whatever MAIL headers are necessary for successful transmission.
   The news article (including its headers) is sent as the body of the
   mail message, with an "N" prepended to each line.

      NOTE: The "N" reduces the probability of an innocent line in a
      news article being taken as a magic command to mail software and
      makes it easy for receiving software to strip off any lines added
      by mail software (e.g., the trailing empty line added by some UUCP
      mail software).

   This method has its weaknesses.  In particular, it assumes that the
   mail transmission channel can transmit nearly arbitrary body text
   undamaged.  When mail is being used as a transmission path of last
   resort, however, the mail system often has inconvenient preconceived
   notions about the format of message bodies.  Various ad hoc encoding
   schemes have been used to avoid such problems.  The recommended
   method is to send a news article or batch as the body of a MIME mail

   message, using content type "application/news-transmission" and
   MIME's "base64" encoding (which is specifically designed to survive
   all known major mail systems).

      NOTE: In the process, MIME conventions could be used to fragment
      and reassemble an article that is too large to be sent as a single
      mail message over a transmission path that restricts message
      length.  In addition, the "conversions" parameter to the content
      type could be used to indicate what (if any) compression method
      has been used.  Also, the Content-MD5 header [RFC1544] can be used
      as a "checksum" to provide high confidence of detecting accidental
      damage to the contents.

      UNRESOLVED ISSUE: The "conversions" parameter no longer exists.
      What should be done about this, if anything?

      NOTE: It might look tempting to use a content type such as
      "message/X-netnews", but MIME bans non-trivial encodings of the
      entire body of messages with content type "message".  The intent
      is to avoid obscuring nested structure underneath encodings.  For
      inter-relayer news transmission, there is no nested structure of
      interest, and it is important that the entire article (including
      its headers, not just its body) be protected against the vagaries
      of intervening mail software.  This situation appears to fit the
      MIME description of circumstances in which "application" is the
      proper content type.

      NOTE: "application/news-transmission", with a "conversions"
      parameter, was registered as a standard subtype by IANA
      22 June 1993.

      UNRESOLVED ISSUE: The "conversions" parameter no longer exists in
      MIME.  What should we do about this?

8.4.  Partial Batches

      UNRESOLVED ISSUE: The existing batch conventions assemble
      (potentially) many articles into one batch.  Handling very large
      articles would be substantially less troublesome if there was also
      a fragmentation convention for splitting a large article into
      several batches.  Is this worth defining at this time?

9.  Propagation and Processing

   Most aspects of news propagation and processing are implementation-
   specific.  The basic propagation algorithms, and certain details of
   how they are implemented, nevertheless need to be standard.

   There are two important principles that news implementors (and
   administrators) need to keep in mind.  The first is the well-known
   Internet Robustness Principle:

      Be liberal in what you accept, and conservative in what you send.

   However, in the case of news there is an even more important
   principle, derived from a much older code of practice, the
   Hippocratic Oath (we will thus call this the Hippocratic Principle):

      First, do no harm.

   It is VITAL to realize that decisions that might be merely suboptimal
   in a smaller context can become devastating mistakes when amplified
   by the actions of thousands of hosts within a few hours.

9.1.  Relayer General Issues

   Relayers MUST NOT alter the content of articles unnecessarily.  Well-
   intentioned attempts to "improve" headers, in particular, typically
   do more harm than good.  It is necessary for a relayer to prepend its
   own name to the Path content (see Section 5.6) and permissible for it
   to rewrite or delete the Xref header (see Section 6.12).  Relayers
   MAY delete the thoroughly obsolete headers described in Appendix A.3,
   although this behavior no longer seems useful enough to encourage.
   Other alterations SHOULD be avoided at all costs, as per the
   Hippocratic Principle.

      NOTE: As discussed in Section 2.3, tidying up the headers of a
      user-prepared article is the job of the posting agent, not the
      relayer.  The relayer's purpose is to move already-compliant
      articles around efficiently without damaging them.  Note that in
      existing implementations, specific programs may contain both
      posting-agent functions and relayer functions.  The distinction is
      that posting-agent functions are invoked only on articles posted
      by local posters, never on articles received from other relayers.

      NOTE: A particular corollary of this rule is that relayers should
      not add headers unless truly necessary.  In particular, this is
      not SMTP; do not add Received headers.

   Relayers MUST NOT pass non-conforming articles on to other relayers,
   except perhaps in a cooperating subnet that has agreed to permit
   certain kinds of non-conforming behavior.  This is a direct
   consequence of the Internet Robustness Principle.

   The two preceding paragraphs may appear to be in conflict.  What is
   to be done when a non-conforming article is received?  The Robustness
   Principle argues that it should be accepted but must not be passed on
   to other relayers while still non-conforming, and the Hippocratic
   Principle strongly discourages attempts at repair.  The conclusion
   that this appears to lead to is correct: a non-conforming article MAY
   be accepted for local filing and processing, or it MAY be discarded
   entirely, but it MUST NOT be passed on to other relayers.

   A relayer MUST NOT respond to the arrival of an article by sending
   mail to any destination, other than a local administrator, except by
   explicit prearrangement with the recipient.  Neither posting an
   article (other than certain types of control messages; see
   Section 7.5) nor being the moderator of a moderated newsgroup
   constitutes such prearrangement.  UNDER NO CIRCUMSTANCES WHATSOEVER
   may a relayer attempt to send mail to either an article's originator
   or a moderator.

      NOTE: Reporting apparent errors in message composition is the job
      of a posting agent, not a relayer.  The same is true of mailing
      moderated-newsgroup postings to moderators.  In networks of
      thousands of cooperating relayers, it is simply unacceptable for
      there to be any circumstance whatsoever that causes any
      significant fraction of them to simultaneously send mail to the
      same destination.  (Some control messages are exceptions, although
      perhaps ill-advised ones.)  What might, in a smaller network, be a
      useful notification or forwarding becomes a deluge of nearly
      identical messages that can bring mail software to its knees and
      severely inconvenience recipients.  Moderators, in particular,
      historically have suffered grievously from this.

   Notification of problems in incoming articles MAY go to local
   administrators, or at most (by prearrangement!)  to the
   administrators of the neighboring relayer(s) that passed on the
   problematic articles.

      NOTE: It would be desirable to notify the author that his posting
      is not propagating as he expects.  However, there is no known
      method for doing this that will scale up gracefully.  (In
      particular, "notify only if within N relayers of the originator"
      falls down in the presence of commercial news services like UUNET:
      there may be hundreds or thousands of relayers within a couple of
      hops of the originator.)  The best that can be done right now is
      to notify neighbors, in hopes that the word will eventually
      propagate up the line, or organize regional monitoring at major
      hubs.

   If it is necessary to alter an article, e.g., translate it to another
   character set or alter its EOL representation, strenuous efforts
   should be made to ensure that such transformations are reversible,
   and that relayers or other software that might wish to reverse them
   know exactly how to do so.

      NOTE: For example, a cooperating subnet that exchanges articles
      using a non-ASCII character set like EBCDIC should define a
      standard, reversible ASCII-EBCDIC mapping and take pains to see
      that it is used at all points where the subnet meets the outside.
      If the only reason for using EBCDIC is that the readers typically
      employ EBCDIC devices, it would be more robust to employ ASCII as
      the interchange format and do the transformation in the reading
      and posting agents.

9.2.  Article Acceptance and Propagation

   When a relayer first receives an article, it must decide whether to
   accept it.  (This applies regardless of whether the article arrived
   by itself or as part of a batch, and in principle regardless of
   whether it originated as a local posting or as traffic from another
   relayer.)  In a cooperating subnet with well-controlled propagation
   paths, some of the tests specified here MAY be delegated to centrally
   located relayers; that is, relayers that can receive news ONLY via
   one of the central relayers might simplify acceptance testing based
   on the assumption that incoming traffic has already passed the full
   set of tests at a central relayer.

   The wording that follows is based on a model in which articles arrive
   on a relayer's host before acceptance tests are done.  However,
   depending on the degree of integration of the transport mechanisms
   and the relayer, some or all of these tests MAY be done before the
   article is actually transmitted, so that articles that definitely
   will not be accepted need not be transmitted at all.

   The wording that follows also specifies a particular order for the
   acceptance tests.  While this order is the obvious one, the tests MAY
   be done in any order.

   First, the relayer MUST verify that the article is a legal news
   article, with all mandatory headers present with legal contents.

      NOTE: This check in principle is done by the first relayer to see
      an article, so an article received from another relayer should
      always be legal, but there is enough old software still
      operational that this cannot be taken for granted; see the
      discussion of the Internet Robustness Principle in Section 9.1.

   Second, the relayer MUST determine whether it has already seen this
   article (identified by its message ID).  This is normally done by
   retaining a history of all article message IDs seen in the last
   N days, where the value of N is decided by the relayer's
   administrator but SHOULD be at least 7.  Since N cannot practically
   be infinite, articles whose Date content indicates that they are
   older than N days are declared "stale" and are deemed to have been
   seen already.

      NOTE: This check is important because news propagation topology is
      typically redundant, often highly so, and it is not at all
      uncommon for a relayer to receive the same article from several
      neighbors.  The history of already-seen message IDs can get quite
      large, hence, the desire to limit its length, but it is important
      that it be long enough that slowly propagating articles are not
      classed as stale.  News propagation within the Internet is
      normally very rapid, but when UUCP links are involved, end-to-end
      delays of several days are not rare, so a week is not a
      particularly generous minimum.

      NOTE: Despite generally more rapid propagation in recent times, it
      is still not unheard of for some propagation paths to be very
      slow.  This can introduce the possibility of old articles arriving
      again after they are gone from the history, hence the "stale"
      rule.

   Third, the relayer MUST determine whether any of the article's
   newsgroups are "subscribed to" by the host, i.e., fit a description
   of what hierarchies or newsgroups the site wants to receive.

      NOTE: This check is significant because information on what
      newsgroups a relayer wishes to receive is often stored at its
      neighbors, who may not have up-to-date information or may simplify
      the rules for implementation reasons.  As a hedge against the
      possibility of missed or delayed newgroup control messages,
      relayers may wish to observe a notion of a newsgroup subscription
      that is independent of the list of newsgroups actually known to
      the relayer.  This would permit reception and relaying of articles
      in newsgroups that the relayer is not (yet) aware of, subject to
      more general criteria indicating that they are likely to be of
      interest.

   Once an article has been accepted, it may be passed on to other
   relayers.  The fundamental news propagation rule is a flooding
   algorithm: on receiving and accepting an article, send it to all
   neighboring relayers not already in its path list that are sent its
   newsgroup(s) and distribution(s).

      NOTE: The path list's role in loop prevention may appear
      relatively unimportant, given that looping articles would
      typically be rejected as duplicates anyway.  However, the path
      list's role in preventing superfluous transmissions is not
      trivial.  In particular, the path list is the only thing that
      prevents relayer X, on receiving an article from relayer Y, from
      sending it back to Y again.  (Indeed, the usual symptom of
      confusion about relayer names is that incoming news loops back in
      this manner.)  The looping articles would be rejected as
      duplicates, but doubling the communications load on every news
      transmission path is not to be taken lightly!

   In general, relayers SHOULD NOT make propagation decisions by
   "anticipation": relayer X, noting that the article's path list
   already contains relayer Y, decides not to send it to relayer Z
   because X anticipates that Z will get the article by a better path.
   If that is generally true, then why is there a news feed from X to Z
   at all?  In fact, the "better path" may be running slowly or may be
   down.  News propagation is very robust precisely because some
   redundant transmission is done "just in case".  If it is imperative
   to limit unnecessary traffic on a path, use of NNTP [RFC977] or
   ihave/sendme (see Section 7.2) to pass articles only when necessary
   is better than arbitrary decisions not to pass articles at all.

   Anticipation is occasionally justified in special cases.  Such cases
   should involve both (1) a cooperating subnet whose propagation paths
   are well-understood and well-monitored, with failures and slowdowns
   noticed and dealt with promptly, and (2) a persistent pattern of
   heavy unnecessary traffic on a path that is either slow or costly.
   In addition, there should be some reason why neither NNTP nor
   ihave/sendme is suitable as a solution to the problem.

9.3.  Administrator Contact

   It is desirable to have a standardized contact address for a
   relayer's administrators, in the spirit of the "postmaster" address
   for mail administrators.  Mail addressed to "newsmaster" on a
   relayer's host MUST go to the administrator(s) of that relayer.  Mail
   addressed to "usenet" on the relayer's host SHOULD be handled
   likewise.  Mail addressed to either address on other hosts using the
   same news database SHOULD be handled likewise.

      NOTE: These addresses are case-sensitive, although it would be
      desirable for sequences equivalent to them using case-insensitive
      comparison to be handled likewise.  While "newsmaster" seems the
      preferred network-independent address, by analogy to "postmaster",
      there is an existing practice of using "usenet" for this purpose,

      and so "usenet" should be supported if at all possible (especially
      on hosts belonging to Usenet!).  The address "news" is also
      sometimes used for purposes like this, but less consistently.

10.  Gatewaying

   Gatewaying of traffic between news networks using this Draft and
   those using other exchange mechanisms can be useful but must be done
   cautiously.  Gateway administrators are taking on significant
   responsibilities and must recognize that the consequences of error
   can be quite serious.

10.1.  General Gatewaying Issues

   This section will primarily address the problems of gatewaying
   traffic INTO news networks.  Little can be said about the other
   direction without some specific knowledge of the network(s) involved.
   However, the two issues are not entirely independent: if a non-news
   network is gatewayed into a news network at more than one point,
   traffic injected into the non-news network by one gateway may appear
   at another as a candidate for injection back into the news network.

   This raises a more general principle, the single most important issue
   for gatewaying:

      Above all, prevent loops.

   The normal loop prevention of news transmission is vitally dependent
   on the Message-ID header.  Any gateway that finds it necessary to
   remove this header, alter it, or supersede it (by moving it into the
   body) MUST take equally effective precautions against looping.

      NOTE: There are few things more effective at turning news readers
      into a lynch mob than a malfunctioning gateway, or pair of
      gateways, that takes in news articles, mangles them just enough to
      prevent news relayers from recognizing them as duplicates, and
      regurgitates them back into the news stream.  This happens rather
      too often.

   Gateway implementors should realize that gateways have all of the
   responsibilities of relayers, plus the added complications introduced
   by transformations between different information formats.  Much of
   the discussion in Section 9 about relayer issues is relevant to
   gateways as well.  In particular, gateways SHOULD keep a history of
   recently seen articles, as described in Section 9.2, and not assume
   that articles will never reappear.  This is particularly important
   for networks that have their own concept analogous to message IDs: a
   gateway should keep a history of traffic seen from BOTH directions.

   If at all possible, articles entering the non-news network SHOULD be
   marked in some way so that they will NOT be re-gatewayed back into
   news.  Multiple gateways obviously must agree on the marking method
   used; if it is done by having them know each others' names, name
   changes MUST be coordinated with great care.  If marking cannot be
   done, all transformations MUST be reversible so that a re-gatewayed
   article is identical to the original (except perhaps for a longer
   Path header).

   Gateways MUST NOT pass control messages (articles containing Control,
   Also-Control, or Supersedes headers) without removing the headers
   that make them control messages, unless there are compelling reasons
   to believe that they are relevant to both sides and that conventions
   are compatible.  If it is truly desirable to pass them unaltered,
   suitable precautions MUST be taken to ensure that there is NO
   POSSIBILITY of a looping control message.

      NOTE: The damage done by looping articles is multiplied a
      thousandfold if one of the affected articles is something like a
      sendsys message (see Section 7.5) that requests multiple automatic
      replies.  Most gateways simply should not pass control messages at
      all.  If some unusual reason dictates doing so, gateway
      implementors and administrators are urged to consider bulletproof
      rate-limiting measures for the more destructive ones like sendsys,
      e.g., passing only one per hour no matter how many are offered.

   Gateways, like relayers, SHOULD make determined efforts to avoid
   mangling articles unnecessarily.  In the case of gateways, some
   transformations may be inevitable, but keeping them to a minimum and
   ensuring that they are reversible is still highly desirable.

   Gateways MUST avoid destroying information.  In particular, the
   restrictions of Section 4.2.2 are best taken with a grain of salt in
   the context of gateways.  Information that does not translate
   directly into news headers SHOULD be retained, perhaps in "X-"
   headers, both because it may be of interest to sophisticated readers
   and because it may be crucial to tracing propagation problems.

   Gateway implementors should take particular note of the discussion of
   mailed replies, or more precisely the ban on same, in Section 9.1.
   Gateway problems MUST be reported to the local administration, not to
   the innocent originator of traffic.  "Gateway problems" here includes
   all forms of propagation anomaly on the non-news side of the gateway,
   e.g., unreachable addresses on a mailing list.  Note that this
   requires consideration of possible misbehavior of "downstream" hosts,
   not just the gateway host.

10.2.  Header Synthesis

   News articles prepared by gateways MUST be legal news articles.  In
   particular, they MUST include all of the mandatory headers (see
   Section 5) and MUST fully conform to the restrictions on said
   headers.  This often requires that a gateway function not only as a
   relayer but also partly as a posting agent, aiding in the synthesis
   of a conforming article from non-conforming input.

      NOTE: The full-conformance requirement needs particularly careful
      attention when gatewaying mailing lists to news, because a number
      of constructs that are legal in MAIL headers are NOT permissible
      in news headers.  (Note also that not all mail traffic fully
      conforms to even the MAIL specification.)  The rest of this
      section will be phrased in terms of mail-to-news gatewaying, but
      most of it is more generally applicable.

   The mandatory headers generally present few problems.

   If no date information is available, the gateway should supply a Date
   header with the gateway's current date.  If only partial information
   is available (e.g., date but not time), this should be fleshed out to
   a full Date header by adding default values, not by mixing in parts
   of the gateway's current date.  (Defaults should be chosen so that
   fleshed-out dates will not be in the future!)  It may be necessary to
   map time zone information to the restricted forms permitted in the
   news Date header.  See Section 5.1.

      NOTE: The prohibition of mixing dates is on the theory that it is
      better to admit ignorance than to lie.

   If the author's address as supplied in the original message is not
   suitable for inclusion in a From header, the gateway MUST transform
   it so it is (for example, by use of the "% hack" and the domain
   address of the gateway).  The desire to preserve information is NOT
   an excuse for violating the rules.  If the transformation is drastic
   enough that there is reason to suspect loss of information, it may be
   desirable to include the original form in an "X-" header, but the
   From header's contents MUST be as specified in Section 5.2.

   If the message contains a Message-ID header, the contents should be
   dealt with as discussed in Section 10.3.  If there is no message ID
   present, it will be necessary to synthesize one, following the news
   rules (see Section 5.3).

   Every effort should be made to produce a meaningful Subject header;
   see Section 5.4.  Many news readers select articles to read based on
   Subject headers, and inserting a placeholder like "<no subject

   available>" is considered highly objectionable.  Even synthesizing a
   Subject header by picking out the first half-dozen nouns and
   adjectives in the article body is better than using a placeholder,
   since it offers SOME indication of what the article might contain.

   The contents of the Newsgroups header (Section 5.5) are usually
   predetermined by gateway configuration, but a gateway to a network
   that has its own concept of newsgroups or discussions might have to
   make transformations.  Such transformations should be reversible;
   otherwise, confusion is likely on both sides.

   It will rarely be possible for gateways to provide a Path header that
   is both an accurate history of the relayers the article has passed
   through AS NEWS and a usable reply address.  The history function
   MUST be given priority; see the discussion in Section 5.6.  It will
   usually be necessary for a gateway to supply an empty path list,
   abandoning the reply function.

   It is desirable for gatewayed articles to convey as much useful
   information as possible, e.g., by use of optional news headers (see
   Section 6) when the relevant information is available.  Synthesis of
   optional headers can generally follow similar rules.

   Software synthesizing References headers should note the discussion
   in Section 6.5 concerning the incompatibility between MAIL and news.
   Also of interest is the possibility of incorporating information from
   In-Reply-To headers and from attribution lines in the body; an
   incomplete or somewhat conjectural References header is much better
   than none at all, and reading agents already have to cope with
   incomplete or slightly erroneous References lists.

10.3.  Message ID Mapping

   This section, like the previous one, is phrased in terms of mail
   being gatewayed into news, but most of the discussion should be more
   generally applicable.

   A particularly sticky problem of gatewaying mail into news is
   supplying legal news message IDs.  Note, in particular, that not all
   MAIL message IDs are legal in news; the news syntax (specified in
   Section 5.3, with related material in Section 5.2) is more
   restrictive.  Generating a fully conforming news article from a mail
   message may require transforming the message ID somewhat.

   Generation and transformation of message IDs assumes particular
   importance if a given mailing list (or whatever) is being handled by
   more than one gateway.  It is highly desirable that the same article
   contents not appear twice in the same newsgroup, which requires that

   they receive the same message ID from all gateways.  Gateways SHOULD
   use the following algorithm (possibly modified by the later
   discussion of gatewaying into more than one newsgroup) unless local
   considerations dictate another:

      1. Separate message ID from surroundings, if necessary.  A
         plausible method for this is to start at the first "<", end at
         the next ">", and reject the message if no ">" is found or a
         second "<" is seen before the ">".  Also reject the message if
         the message ID contains no "@" or more than one "@", or if it
         contains no ".".  Also reject the message if the message ID
         contains non-ASCII characters, ASCII control characters, or
         white space.

            NOTE: Any legitimate domain will include at least one ".".
            [RFC822], Section 6.2.2, forbids white space in this context
            when passing mail on to non-MAIL software.

      2. Delete the leading "<" and trailing ">".  Separate message ID
         into local part and domain at the "@".

      3. In both components, transliterate leading dots (".", ASCII 46),
         trailing dots, and dots after the first in sequences of two or
         more consecutive dots, into underscores (ASCII 95).

      4. In both components, transliterate disallowed characters other
         than dots (see the definition of <unquoted-char> in
         Section 5.2) to underscores (ASCII 95).

      5. Form the message ID as

            "<" local-part "@" domain ">"

      NOTE: This algorithm is approximately that of Rich Salz's
      successful gatewaying package.

   Despite the desire to keep message IDs consistent across multiple
   gateways, there is also a more subtle issue that can require a
   different approach.  If the same articles are being gatewayed into
   more than one newsgroup, and it is not possible to arrange that all
   gateways gateway them to the same cross-posted set of newsgroups,
   then the message IDs in the different newsgroups MUST be DIFFERENT.

      NOTE: Otherwise, arrival of an article in one newsgroup will
      prevent it from appearing in another, and which newsgroup a
      particular article appears in will be an accident of which
      direction it arrives from first.  It is very difficult to maintain
      a coherent discussion when each participant sees a randomly

      selected 50% of the traffic.  The fundamental problem here is that
      the basic assumption behind message IDs is being violated: the
      gateways are assigning the same message ID to articles that differ
      in an important respect (Newsgroups header).

   In such cases, it is suggested that the newsgroup name, or an agreed-
   on abbreviation thereof, be prepended to the local part of the
   message ID (with a separating ".") by the gateway.  This will ensure
   that multiple gateways generate the same message ID, while also
   ensuring that different newsgroups can be read independently.

      NOTE: It is preferable to have the gateway(s) cross-post the
      article, avoiding the issue altogether, but this may not be
      feasible, especially if one newsgroup is widespread and the other
      is purely local.

10.4.  Mail to and from News

   Gatewaying mail to news, and vice versa, is the most obvious form of
   news gatewaying.  It is common to set up gateways between news and
   mail rather too casually.

   It is hard to go very wrong in gatewaying news into a mailing list,
   except for the non-trivial matter of making sure that error reports
   go to the local administration rather than to the authors of news
   articles.  (This requires attention to the "envelope address" as well
   as to the message headers.)  Doing the reverse connection correctly
   is much harder than it looks.

      NOTE: In particular, just feeding the mail message to "inews -h"
      or the equivalent is NOT, repeat NOT, adequate to gateway mail to
      news.  Significant gatewaying software is necessary to do it
      right.  Not all headers of mail messages conform to even the MAIL
      specifications, never mind the stricter rules for news.

   It is useful to distinguish between two different forms of
   mail-to-news gatewaying: gatewaying a mailing list into a newsgroup,
   and operating a "post-by-mail" service in which individual articles
   can be posted to a newsgroup by mailing them to a specific address.
   In the first case, the message is already being "broadcast", and the
   situation can be viewed as gatewaying one form of news into another.
   The second case is closer to that of a moderator posting submissions
   to a moderated newsgroup.

   In either case, the discussions in the preceding two sections are
   relevant, as is the Hippocratic Principle of Section 9.  However,
   some additional considerations are specific to mail-to-news
   gatewaying.

   As mentioned in Section 6, point-to-point headers like To and Cc
   SHOULD NOT appear as such in news, although it is suggested that they
   be transformed to "X-" headers, e.g., X-To and X-Cc, to preserve
   their information content for possible use by readers or
   troubleshooters.  The Received header is entirely specific to MAIL
   and SHOULD be deleted completely during gatewaying, except perhaps
   for the Received header supplied by the gateway host itself.

   The Sender header is a tricky case, one where mailing-list and post-
   by-mail practice should differ.  For gatewaying mailing lists, the
   mailing-list host should be considered a relayer, and the From and
   Sender headers supplied in its transmissions left strictly untouched.
   For post-by-mail, as for a moderator posting a mailed submission, the
   Sender header should reflect the poster rather than the author.  If a
   post-by-mail gateway receives a message with its own Sender header,
   it might wish to preserve the content in an X-Sender header.

   It will generally be necessary to transform between mail's
   In-Reply-To/References convention and news's References/See-Also
   convention, to preserve correct semantics of cross references.  This
   also requires attention when going the other way, from news to mail.
   See the discussion of the difference in Section 6.5.

10.5.  Gateway Administration

   Any news system will benefit from an attentive administrator,
   preferably assisted by automated monitoring for anomalies.  This is
   particularly true of gateways.  Gateway software SHOULD be
   instrumented so that unusual occurrences, such as sudden massive
   surges in traffic, are reported promptly.  It is desirable, in fact,
   to go further: gateway software SHOULD endeavor to limit damage in
   the event that the administrator does not respond promptly.

      NOTE: For example, software might limit the gatewaying rate by
      queueing incoming traffic and emptying the queue at a finite
      maximum rate (well below the maximum that the host is capable of!)
      that is set by the administrator and is not raised automatically.

   Traffic gatewayed into a news network SHOULD include a suitable
   header, perhaps X-Gateway-Administrator, giving an electronic address
   that can be used to report problems.  This SHOULD be an address that
   goes directly to a human, and not to a "routine administrative
   issues" mailbox that is examined only occasionally, since the point
   is to be able to reach the administrator quickly in an emergency.
   Gateway administrators SHOULD arrange substitutes to cover gateway
   operation (with suitable redirection of mail) when they are on
   vacation, etc.

11.  Security and Related Issues

   Although the interchange format itself raises no significant security
   issues, the wider context does.

11.1.  Leakage

   The most obvious form of security problem with news is "leakage" of
   articles that are intended to have only restricted circulation.  The
   flooding algorithm is EXTREMELY good at finding any path by which
   articles can leave a subnet with supposedly restrictive boundaries.
   Substantial administrative effort is required to ensure that local
   newsgroups remain local, unless connections to the outside world are
   tightly restricted.

   A related problem is that the sendme control message can be used to
   ask for any article by its message ID.  The usefulness of this has
   declined as message-ID generation algorithms have become less
   predictable, but it remains a potential problem for "secure"
   newsgroups.  Hosts with such newsgroups may wish to disable the
   sendme control message entirely.

   The sendsys, version, and whogets control messages also allow
   "outsiders" to request information from "inside", which may reveal
   details of internal topology (etc.)  that are considered
   confidential.  (Note that at least limited openness about such
   matters may be a condition of membership in such networks, e.g.,
   Usenet.)

   Organizations wishing to control these forms of leakage are strongly
   advised to designate a small number of "official gateway" hosts to
   handle all news exchange with the outside world, so that a bounded
   amount of administrative effort is needed to control propagation and
   eliminate problems.  Attempts to keep news out entirely, by refusing
   to support an official gateway, typically result in large numbers of
   unofficial partial gateways appearing over time.  Such a
   configuration is much more difficult to troubleshoot.

   A somewhat related problem is the possibility of proprietary material
   being disclosed unintentionally by a poster who does not realize how
   far his words will propagate, either from sheer misunderstanding or
   because of errors made (by human or software) in followup
   preparation.  There is little that can be done about this except
   education.

11.2.  Attacks

   Although the limitations of the medium restrict what can be done to
   attack a host via news, some possibilities exist, most of them
   problems news shares with mail.

   If reading agents are careless about transmitting non-printable
   characters to output devices, malicious posters may post articles
   containing control sequences ("letterbombs") meant to have various
   destructive effects on output devices.  Possible effects depend on
   the device, but they can include hardware damage (e.g., by repeated
   writing of values into configuration memories that can tolerate only
   a limited number of write cycles) and security violation (e.g., by
   reprogramming function keys potentially used by privileged readers).

   A more sophisticated variation on the letterbomb is inclusion of
   "Trojan horses" in programs.  Obviously, readers must be cautious
   about using software found in news, but more subtly, reading agents
   must also exercise care.  MIME messages can include material that is
   executable in some sense, such as PostScript documents (which are
   programs!), and letterbombs may be introduced into such material.

   Given the presence of finite resources and other software
   limitations, some degree of system disruption can be achieved by
   posting otherwise-innocent material in great volume, either in single
   huge articles (see Section 4.6) or in a stream of modest-sized
   articles.  (Some would say that the steady growth of Usenet volume
   constitutes a subtle and unintentional attack of the latter type;
   certainly it can have disruptive effects if administrators are
   inattentive.)  Systems need some ability to cope with surges, because
   single huge articles occur occasionally as the result of software
   error, innocent misunderstanding, or deliberate malice; and downtime
   at upstream hosts can cause droughts, followed by floods, of
   legitimate articles.  (There is also a certain amount of normal
   variation; for example, Usenet traffic is noticeably lighter on
   weekends and during Christmas holidays, and rises noticeably at the
   start of the school term of North American universities.)  However, a
   site that normally receives little traffic may be quite vulnerable to
   "swamping" attack if its software is insufficiently careful.

   In general, careless implementation may open doors that are not
   intrinsic to news.  In particular, implementation of control messages
   (see Sections 6.6 and 7) and unbatchers (see Sections 8.1 and 8.2)
   via a command interpreter requires substantial precautions to ensure
   that only the intended capabilities are available.  Care must also be
   taken that article-supplied text is not fed to programs that have
   escapes to command interpreters.

   Finally, there is considerable potential for malice in the sendsys,
   version, and whogets control messages.  They are not harmful to the
   hosts receiving them as news, but they can be used to enlist those
   hosts (by the thousands) as unwitting allies in a mail-swamping
   attack on a victim who may not even receive news.  The precautions
   discussed in Section 7.5 can reduce the potential for such attacks
   considerably, but the hazard cannot be eliminated as long as these
   control messages exist.

11.3.  Anarchy

   The highly distributed nature of news propagation, and the lack of
   adequate authentication protocols (especially for use over the less-
   interactive transport mechanisms such as UUCP), make article forgery
   relatively straightforward.  It may be possible to at least track a
   forgery to its source, once it is recognized as such, but clever
   forgers can make even that relatively difficult.  The assumption that
   forgeries will be recognized as such is also not to be taken for
   granted; readers are notoriously prone to blindly assuming
   authenticity.  If a forged article's initial path list includes the
   relayer name of the supposed poster's host, the article will never be
   sent to that host, and the alleged author may learn about the forgery
   secondhand or not at all.

   A particularly noxious form of forgery is the forged "cancel" control
   message.  Notably, it is relatively straightforward to write software
   that will automatically send out a (forged) cancel message for any
   article meeting some criterion, e.g., written by a specific author.
   The authentication problems discussed in Section 7.1 make it
   difficult to solve this without crippling cancel's important
   functionality.

   A related problem is the possibility of disagreements over newsgroup
   creation, on networks where such things are not decided by central
   authorities.  There have been cases of "rmgroup wars", where one
   poster persistently sends out newgroup messages to create a newsgroup
   and another, equally persistently, sends out rmgroup messages asking
   that it be removed.  This is not particularly damaging, if relayers
   are configured to be cautious, but it can cause serious confusion
   among innocent third parties who just want to know whether or not
   they can use the newsgroup for communication.

11.4.  Liability

   News shares the legal uncertainty surrounding other forms of
   electronic communication: what rules apply to this new medium of
   information exchange?  News is a particularly problematic case

   because it is a broadcast medium rather than a point-to-point one
   like mail, and analogies to older forms of communication are
   particularly weak.

   Are news-carrying hosts common carriers, like the phone companies,
   providing communications paths without having either authority over
   or responsibility for content?  Or are they publishers, responsible
   for the content regardless of whether they are aware of it or not?
   Or something in between?  Such questions are particularly significant
   when the content is technically criminal, e.g., some types of
   sexually oriented material in some jurisdictions, in which case
   ignorance of its presence may not be an adequate defense.

   Even in milder situations such as libel or copyright violation, the
   responsibilities of the poster, his host, and other hosts carrying
   the traffic are unclear.  Note, in particular, the problems arising
   when the article is a forgery, or when the alleged author claims it
   is a forgery but cannot prove this.

12.  References

   [ISO/IEC9899]  "Information technology - Programming Language C",
                  ISO/IEC 9899:1990 {more recently 9899:1999}, 1990.

   [Metamail]     Borenstein, N.,
                  <http://ftp.funet.fi/pub/unix/mail/metamail/ANNOUNCE>,
                  February 1994.

   [RFC821]       Postel, J., "Simple Mail Transfer Protocol", STD 10,
                  RFC 821, August 1982.

   [RFC822]       Crocker, D., "STANDARD FOR THE FORMAT OF ARPA INTERNET
                  TEXT MESSAGES", STD 11, RFC 822, August 1982.

   [RFC850]       Horton, M., "Standard for interchange of Usenet
                  messages", RFC 850, June 1983.

   [RFC977]       Kantor, B. and P. Lapsley, "Network News Transfer
                  Protocol - A Proposed Standard for the Stream-Based
                  Transmission of News", RFC 977, February 1986.

   [RFC1036]      Horton, M. and R. Adams, "Standard for interchange of
                  USENET Messages", RFC 1036, December 1987.

   [RFC1123]      Braden, R., Ed., "Requirements for Internet Hosts -
                  Application and Support", STD 3, RFC 1123,
                  October 1989.

   [RFC1341]      Borenstein, N. and N. Freed, "MIME (Multipurpose
                  Internet Mail Extensions): Mechanisms for Specifying
                  and Describing the Format of Internet Message Bodies",
                  RFC 1341, June 1992.

   [RFC1342]      Moore, K., "Representation of Non-ASCII Text in
                  Internet Message Headers", RFC 1342, June 1992.

   [RFC1345]      Simonsen, K., "Character Mnemonics and Character
                  Sets", RFC 1345, June 1992.

   [RFC1413]      St. Johns, M., "Identification Protocol", RFC 1413,
                  February 1993.

   [RFC1456]      Vietnamese Standardization Working Group, "Conventions
                  for Encoding the Vietnamese Language", RFC 1456,
                  May 1993.

   [RFC1544]      Rose, M., "The Content-MD5 Header Field", RFC 1544,
                  November 1993.

   [RFC1896]      Resnick, P. and A. Walker, "The text/enriched MIME
                  Content-type", RFC 1896, February 1996.

   [RFC2045]      Freed, N. and N. Borenstein, "Multipurpose Internet
                  Mail Extensions (MIME) Part One: Format of Internet
                  Message Bodies", RFC 2045, November 1996.

   [RFC2046]      Freed, N. and N. Borenstein, "Multipurpose Internet
                  Mail Extensions (MIME) Part Two: Media Types",
                  RFC 2046, November 1996.

   [RFC2047]      Moore, K., "MIME (Multipurpose Internet Mail
                  Extensions) Part Three: Message Header Extensions for
                  Non-ASCII Text", RFC 2047, November 1996.

   [RFC2049]      Freed, N. and N. Borenstein, "Multipurpose Internet
                  Mail Extensions (MIME) Part Five: Conformance Criteria
                  and Examples", RFC 2049, November 1996.

   [RFC2822]      Resnick, P., Ed., "Internet Message Format", RFC 2822,
                  April 2001.

   [RFC3977]      Feather, C., "Network News Transfer Protocol (NNTP)",
                  RFC 3977, October 2006.

   [RFC5322]      Resnick, P., Ed., "Internet Message Format", RFC 5322,
                  October 2008.

   [RFC5536]      Murchison, K., Ed., Lindsey, C., and D. Kohn, "Netnews
                  Article Format", RFC 5536, November 2009.

   [RFC5537]      Allbery, R., Ed., and C. Lindsey, "Netnews
                  Architecture and Protocols", RFC 5537, November 2009.

   [Sanderson]    David Sanderson, Smileys, O'Reilly & Associates Ltd.,
                  1993.

   [UUCP]         Tim O'Reilly and Grace Todino, Managing UUCP and
                  Usenet, O'Reilly & Associates Ltd., January 1992.

   [X3.4]         "American National Standard for Information Systems -
                  Coded Character Sets - 7-Bit American National
                  Standard Code for Information Interchange (7-Bit
                  ASCII)", ANSI X3.4, March 1986.

Appendix A.  Archaeological Notes

A.1.  "A News" Article Format

   The obsolete "A News" article format consisted of exactly five lines
   of header information, followed by the body.  For example:

      Aeagle.642
      news.misc
      cbosgd!mhuxj!mhuxt!eagle!jerry
      Fri Nov 19 16:14:55 1982
      Usenet Etiquette - Please Read
      body
      body
      body

   The first line consisted of an "A" followed by an article ID
   (analogous to a message ID and used for similar purposes).  The
   second line was the list of newsgroups.  The third line was the path.
   The fourth was the date, in the format above (all fields fixed
   width), resembling an Internet date but not quite the same.  The
   fifth was the subject.

   This format is documented for archaeological purposes only.  Do not
   generate articles in this format.

A.2.  Early "B News" Article Format

   This obsolete pseudo-Internet article format, used briefly during the
   transition between the A News format and the modern format, followed
   the general outline of a MAIL message but with some non-standard
   headers.  For example:

      From: cbosgd!mhuxj!mhuxt!eagle!jerry (Jerry Schwarz)
      Newsgroups: news.misc
      Title: Usenet Etiquette -- Please Read
      Article-I.D.: eagle.642
      Posted: Fri Nov 19 16:14:55 1982
      Received: Fri Nov 19 16:59:30 1982
      Expires: Mon Jan 1 00:00:00 1990

      body
      body
      body

   The From header contained the information now found in the Path
   header, plus possibly the full name now typically found in the From
   header.  The Title header contained what is now the Subject content.

   The Posted header contained what is now the Date content.  The
   Article-I.D. header contained an article ID, analogous to a message
   ID and used for similar purposes.  The Newsgroups and Expires headers
   were approximately as they are now.  The Received header contained
   the date when the latest relayer to process the article first saw it.
   All dates were in the above format, with all fields fixed width,
   resembling an Internet date but not quite the same.

   This format is documented for archaeological purposes only.  Do not
   generate articles in this format.

A.3.  Obsolete Headers

   Early versions of news software following the modern format sometimes
   generated headers like the following:

      Relay-Version: version B 2.10 2/13/83; site cbosgd.UUCP
      Posting-Version: version B 2.10 2/13/83; site eagle.UUCP
      Date-Received: Friday, 19-Nov-82 16:59:30 EST

   Relay-Version contained version information about the relayer that
   last processed the article.  Posting-Version contained version
   information about the posting agent that posted the article.  Date-
   Received contained the date when the last relayer to process the
   article first saw it (in a slightly nonstandard format).

   These headers are documented for archaeological purposes only.  Do
   not generate articles using them.

A.4.  Obsolete Control Messages

   There once was a senduuname control message, resembling sendsys but
   requesting transmission of the list of hosts to which the receiving
   host had UUCP connections.  This rapidly ceased to be of much use,
   and many organizations consider information about their internal
   connectivity to be confidential.

   Historically, a checkgroups body consisting of one or two lines, the
   first of the form "-n newsgroup", caused checkgroups to apply to only
   that single newsgroup.  This form is documented for archaeological
   purposes only; do not use it.

   Historically, an article posted to a newsgroup whose name had exactly
   three components of which the third was "ctl" signified that article
   was to be taken as a control message.  The Subject header specified
   the actions in the same way the Control header does now.  This form
   is documented for archaeological purposes only; do not use it; do not
   implement it.

Appendix B.  A Quick Tour of MIME

   (The editor wishes to thank Luc Rooijakkers; most of this appendix is
   a lightly edited version of a summary he kindly supplied.)

   MIME (Multipurpose Internet Mail Extensions) is an upward-compatible
   set of extensions to [RFC822], currently documented in [RFC2045],
   [RFC2046], and [RFC2047].  This appendix summarizes these documents.
   See the MIME RFCs for more information; they are very readable.

      UNRESOLVED ISSUE: These RFC numbers (here and elsewhere in this
      Draft) need updating when the new MIME RFCs come out {now
      resolved!}.

   MIME defines the following new headers:

      MIME-Version
      Content-Type
      Content-Transfer-Encoding
      Content-ID
      Content-Description

   The MIME-Version header is mandatory for all messages conforming to
   the MIME specification and carries the version number of the MIME
   specification.  Example:

      MIME-Version: 1.0

   The Content-Type header indicates the content type of the message.
   Content types are split into a top-level type and a subtype,
   separated by a slash.  Auxiliary information can also be supplied,
   using an attribute-value notation.  Example:

      Content-Type: text/plain; charset=us-ascii

   (In the absence of a Content-Type header this is in fact the default
   content type.)

   Important type/subtype combinations are:

   text/plain              Plain text, possibly in a non-ASCII character
                           set.

   text/enriched           A very simple wordprocessor-like language
                           supporting character attributes (e.g.,
                           underlining), justification control, and
                           multiple character sets.  (This proposal has

                           gone through several iterations and has
                           recently split off from the main MIME RFCs
                           into a separate document [RFC1896].)

   message/rfc822          A mail message conforming to a slightly
                           relaxed version of [RFC822].

   message/partial         Part of a message (supporting the transparent
                           splitting and joining of messages when they
                           are too large to be handled by some transport
                           agent).

   message/external-body   A message whose body is external.  Possible
                           access methods include via mail, FTP, local
                           file, etc.

   multipart/mixed         A message whose body consists of multiple
                           parts, possibly of different types, intended
                           to be viewed in serial order.  Each part
                           looks like an [RFC822] message, consisting of
                           headers and a body.  Most of the [RFC822]
                           headers have no defined semantics for body
                           parts.

   multipart/parallel      Likewise, except that the parts are intended
                           to be viewed in parallel (on user agents that
                           support it).

   multipart/alternative   Likewise, except that the parts are intended
                           to be semantically equivalent such that the
                           part that best matches the capabilities of
                           the environment should be displayed.  For
                           example, a message may include plain-text,
                           enriched-text, and postscript versions of
                           some document.

   multipart/digest        A variant of multipart/mixed especially
                           intended for message digests (the default
                           type of the parts is message/rfc822 instead
                           of text/plain, saving on the number of
                           headers for the parts).

   application/postscript  A PostScript document.  (PostScript is a
                           trademark of Adobe.)

   Other top-level types exist for still images, audio, and video
   samples.

   Some of the above types require the ability to transport binary data.
   Since the existing message systems usually do not support this, MIME
   provides a Content-Transfer-Encoding header to indicate the kind of
   encoding used.  The possible encodings are:

   7bit              No encoding; the data consists of short (less than
                     1000 characters) lines of 7-bit ASCII data,
                     delimited by EOL sequences.  This is the default
                     encoding.

   8bit              Like 7bit, except that bytes with the high-order
                     bit set may be present.  Many transmission paths
                     are incapable of carrying messages that use this
                     encoding.

   binary            No encoding; any sequence of bytes may be present.
                     Many transmission paths are incapable of carrying
                     messages that use this encoding.

   base64            The data is encoded by representing every group of
                     3 bytes as 4 characters from the alphabet
                     "A-Za-z0-9+/", which was chosen for its high
                     robustness through mail gateways (the alphabet used
                     by uuencode does not survive ASCII-EBCDIC-ASCII
                     translations).  In the final group of 4 characters,
                     "=" is used for those characters not representing
                     data bytes.  Line length is limited, and EOLs in
                     the encoded form are ignored.

   quoted-printable  Any byte can be represented by a three-character
                     "=XX" sequence where the X's are uppercase
                     hexadecimal digits.  Bytes representing printable
                     7-bit US-ASCII characters except "=" may be
                     represented literally.  Tabs and blanks may be
                     represented literally if not at the end of a line.
                     Line length is limited, and an EOL preceded by "="
                     was inserted for this purpose and is not present in
                     the original.

   The base64 and quoted-printable encodings are applied to data in
   Internet canonical form, which means that any EOL encoded as anything
   but EOL must be an Internet canonical EOL: CR followed by LF.

   The Content-Description header allows further description of a body
   part, analogous to the use of Subject for messages.

   Finally, the Content-ID header can be used to assign an
   identification to body parts, analogous to the assignment of
   identifications to messages by Message-ID.

   Note that most of these headers are structured header fields, as
   defined in [RFC822].  Consequently, comments are allowed in their
   values.  The following is a legal MIME header:

      Content-Type: (a comment) text (yeah)   /
              plain    (and now some params:) ; charset= (guess what)
         iso-8859-1 (we don't have iso-10646 yet, pity)

      NOTE: Although the MIME specification was developed for mail,
      there is nothing precluding its use for news as well.  While it
      might simplify implementation to restrict the MIME headers
      somewhat, in the same way that other news headers (e.g., From) are
      restricted subsets of the [RFC822] originals, this would add yet
      another divergence between two formats that ought to be as
      compatible as possible.  In the case of the MIME headers, there is
      no body of existing code posing compatibility concerns.  A full-
      featured MIME reading agent needs a full [RFC822] parser anyway,
      to properly handle body parts of types like message/rfc822, so
      there is little gain from restricting MIME headers.  Adopting the
      MIME specification unchanged seems best.  However, article-level
      MIME headers must still comply with the overall news header syntax
      given in Section 4, so that news software that is NOT interested
      in MIME need not contain a full [RFC822] parser.

   "MIME (Multipurpose Internet Mail Extensions) Part Three: Message
   Header Extensions for Non-ASCII Text" [RFC2047] addresses the problem
   of non-ASCII characters in headers.  An example of a header using the
   [RFC2047] mechanism is

      From: =?ISO-8859-1?Q?Andr=E9_?= Pirard <PIRARD@vm1.ulg.ac.be>

   Such encodings are allowed in selected headers, subject to the
   restrictions listed in [RFC2047].

   The MIME effort has also produced an RFC defining a Content-MD5
   header [RFC1544] containing an MD5-based "checksum" of the contents
   of an article or body part, giving high confidence of detecting
   accidental modifications to the contents.

   The "metamail" software package [Metamail] helps provide MIME support
   with minimal changes to mailers and may also be relevant to news
   reading agents.

   The PEM (Privacy Enhanced Mail) effort is pursuing analogous
   facilities to offer stronger guarantees against malicious
   modifications, unauthorized eavesdropping, and forgery.  This work
   too may be applicable to news, once it is reconciled with MIME (by
   efforts now underway).

Appendix C.  Summary of Changes Since RFC 1036

   This Draft is much longer than [RFC1036], so there is obviously much
   change in content.  Much of this is just increased precision and
   rigor.  Noteworthy changes and additions include:

      + restrictions on article bodies (Section 4.3)

      + all references to MIME facilities

      + size limits on articles

      + precise specification of Date-content syntax

      + message IDs must never be re-used, ever

      + "!" is the only Path delimiter

      + multiple moderators in the Approved header

      + rules on References trimming, and the _-_ mechanism

      + generalization of the Xref rules

      + multiple message IDs in Cancel and Supersedes

      + Also-Control

      + See-Also

      + Article-Names

      + Article-Updates

      + more precise rules for cancellation

      + cancellation authorization based on From, not Sender

      + "unmoderated" and descriptors in newgroup messages

      + restrictive rules on handling of sendsys and version messages

      + the whogets control message

      + precise specification of checkgroups messages

      + compression type preferably specified out-of-band

      + rules for encapsulating news in MIME mail

      + tighter specification of relayer functioning (Section 9.1)

      + the "newsmaster" contact address

      + rules for gatewaying (Section 10)

      + discussion of security issues (Section 11)

Appendix D.  Summary of Completely New Features

   Most of this Draft merely documents existing practice, preferred
   versions thereof, or straightforward generalizations of it, but there
   are a few outright inventions.  These are:

      + the _-_ mechanism for References trimming

      + Also-Control

      + See-Also

      + Article-Names

      + Article-Updates

      + the whogets control message

Appendix E.  Summary of Differences from RFCs 822 and 1123

   The following are noteworthy differences between this Draft's
   articles and MAIL messages:

      + generally less-permissive header syntax

      + notably, limited From syntax

      + MAIL header comments allowed in only a few contexts

      + slightly more restricted message-ID syntax

      + several more mandatory headers

      + duplicate headers forbidden

      + References/See-Also versus In-Reply-To/References (Section 6.5)

      + case sensitivity in some contexts

      + point-to-point headers, e.g., To and Cc, forbidden (Section 6)

      + several new headers

Author's Address

   Henry Spencer
   SP Systems
   Box 280 Stn. A
   Toronto, Ontario M5W1B2
   Canada

   EMail: henry@zoo.utoronto.ca