6. Optional Headers
Many MAIL headers, and many of those specified in present and future
MAIL extensions, are potentially applicable to news. Headers
specific to MAIL's point-to-point transmission paradigm, e.g., To and
Cc, SHOULD NOT appear in news articles. (Gateways wishing to
preserve such information for debugging probably SHOULD hide it under
different names; prefixing "X-" to the original headers, resulting in
forms like "X-To", is suggested.)
The following optional headers are either specific to news or of
particular note in news articles; an article MAY contain some or all
of them. (Note that there are some circumstances in which some of
them are mandatory; these are explained under the individual
headers.) An article MUST NOT contain two or more headers with any
one of these header names.
NOTE: The ban on duplicate header names does not apply to headers
not specified in this Draft, such as "X-" headers. Software
should not assume that all header names in a given article are
The Followup-To header contents specify to which newsgroup(s)
followups should be posted:
Followup-To-content = Newsgroups-content / "poster"
The syntax is the same as that of the Newsgroups content, with the
exception that the magic word "poster" means that followups should be
mailed to the article's reply address rather than posted. In the
absence of Followup-To, the default newsgroup(s) for a followup are
those in the Newsgroups header.
NOTE: The way to request that followups be mailed to a specific
address other than that in the From line is to supply
"Followup-To: poster" and a Reply-To header. Putting a mailing
address in the Followup-To line is incorrect; posting agents
should reject or rewrite such headers.
NOTE: There is no syntax for "no followups allowed" because
"Followup-To: poster" accomplishes this effect without extra
Although it is generally desirable to limit followups to the smallest
reasonable set of newsgroups, especially when the precursor was
cross-posted widely, posting agents SHOULD NOT supply a Followup-To
header except at the poster's explicit request.
NOTE: In particular, it is incorrect for the posting agent to
assume that followups to a cross-posted article should be directed
to the first newsgroup only. Trimming the list of newsgroups
should be the poster's decision, not the posting agent's.
However, when an article is to be cross-posted to a considerable
number of newsgroups, a posting agent might wish to SUGGEST to the
poster that followups go to a shorter list.
The Expires header content specifies a date and time when the article
is deemed to be no longer useful and should be removed ("expired"):
Expires-content = Date-content
The content syntax is the same as that of the Date content. In the
absence of Expires, the default is decided by the administrators of
each host the article reaches, who MAY also restrict the extent to
which the Expires header is honored.
The Expires header has two main applications: removing articles whose
utility ends on a specific date (e.g., event announcements that can
be removed once the day of the event has passed) and preserving
articles expected to be of prolonged usefulness (e.g., information
aimed at new readers of a newsgroup). The latter application is
sometimes abused. Since individual hosts have local policies for
expiration of news (depending on available disk space, for instance),
posters SHOULD NOT provide Expires headers for articles unless there
is a natural expiration date associated with the topic. Posting
agents MUST NOT provide a default Expires header. Leave it out and
allow local policies to be used unless there is a good reason not to.
Expiry dates are properly the decision of individual host
administrators; posters and moderators SHOULD set only expiry dates
with which most administrators would agree.
NOTE: A poster preparing an Expires header for an article whose
utility ends on a specific day should typically specify the NEXT
day as the expiry date. A meeting on July 7th remains of interest
on the 7th.
The Reply-To header content specifies a reply address different from
the author's address given in the From header:
Reply-To-content = From-content
In the absence of Reply-To, the reply address is the address in the
Use of a Reply-To header is preferable to including a similar request
in the article body, because reply-preparation software can take
account of Reply-To automatically.
The Sender header identifies the poster, in the event that this
differs from the author identified in the From header:
Sender-content = From-content
In the absence of Sender, the default poster is the author (named in
the From header).
NOTE: The intent is that the Sender header have a fairly high
probability of identifying the person who really posted the
article. The ability to specify a From header naming someone
other than the poster is useful but can be abused.
If the poster supplies a From header, the posting agent MUST ensure
that a Sender header is present, unless it can verify that the
mailing address in the From header is a valid mailing address for the
poster. A poster-supplied Sender header MAY be used, if its mailing
address is verifiably a valid mailing address for the poster;
otherwise, the posting agent MUST supply a Sender header and delete
(or rename, for example, to X-Unverifiable-Sender) any poster-
supplied Sender header.
NOTE: It might be useful to preserve a poster-supplied Sender
header so that the poster can supply the full-name part of the
content. The mailing address, however, must be right, hence, the
posting agent must generate the Sender header if it is unable to
verify the mailing address of a poster-supplied one.
NOTE: NNTP implementors, in particular, are urged to note this
requirement (which would eliminate the need for ad hoc headers
like NNTP-Posting-Host), although there are admittedly some
implementation difficulties. A user name from an [RFC1413] server
and a host name from an inverse mapping of the address, perhaps
with a "full name" comment noting the origin of the information,
would be at least a first approximation:
Sender: firstname.lastname@example.org (RFC-1413@reverse-lookup;
While this does not completely meet the specs, it comes a lot closer
than not having a Sender header at all. Even just supplying a
placeholder for the user name:
Sender: email@example.com (user name unknown)
would be better than nothing.
The References header content lists message IDs of precursors:
References-content = message-id *( space message-id )
A followup MUST have a References header, and an article that is not
a followup MUST NOT have a References header. The References-content
of a followup MUST be the precursor's References-content (if any)
followed by the precursor's message ID.
NOTE: Use the See-Also header (Section 6.16) for interconnection
of articles that are not in a followup relationship to each other.
NOTE: In retrospect, RFCs 850 and 1036, and the implementations
whose practice they represented, erred here. The proper MAIL
header to use for references to precursors is In-Reply-To, and the
References header is meant to be used for the purposes here
ascribed to See-Also. This incompatibility is far too solidly
established to be fixed, unfortunately. The best that can be done
is to provide a clear mapping between the two and urge gateways to
do the transformation. The news usage is (now) a deliberate
violation of the MAIL specifications; articles containing news
References headers are technically not valid MAIL messages,
although it is unlikely that much MAIL software will notice
because the incompatibility is at a subtle semantic level that
does not affect the syntax.
UNRESOLVED ISSUE: Would it be better to just give up and admit
that news uses References for both purposes?
UNRESOLVED ISSUE: Should the syntax be generalized to include URLs
as alternatives to message IDs? Perhaps not; too many things know
about References already. And non-articles can't be precursors of
articles, not really.
Followup agents SHOULD NOT shorten References headers. If it is
absolutely necessary to shorten the header, as a desperate last
resort, a followup agent MAY do this by deleting some of the message
IDs. However, it MUST NOT delete the first message ID, the last
three message IDs (including that of the immediate precursor), or any
message ID mentioned in the body of the followup. If it is possible
for the followup agent to determine the Subject content of the
articles identified in the References header, it MUST NOT delete the
message ID of any article where the Subject content changed (other
than by prepending of a back reference). The followup agent MUST NOT
delete any message ID whose local part ends with "_-_" (underscore
(ASCII 95), hyphen (ASCII 45), underscore); followup agents are urged
to use this form to mark subject changes and to avoid using it
NOTE: As software capable of exploiting References chains has
grown more common, the random shortening permitted by [RFC1036]
has become increasingly troublesome. ANY shortening is
undesirable, and software should do it only in cases of dire
necessity. In such cases, these rules attempt to limit the
NOTE: The first message ID is very important as the starting point
of the "thread" of discussion and absolutely should not be
deleted. Keeping the last three message IDs gives thread-
following software a fighting chance to reconstruct a full thread
even if an article or two is missing. Keeping message IDs
mentioned in the body is obviously desirable.
NOTE: Subject changes are difficult to determine, but they are
significant as possible beginnings of new threads. The "_-_"
convention is provided so that posting agents (which have more
information about subjects) can flag articles containing a subject
change in a way that followup agents can detect without access to
the articles themselves. The sequence is chosen as one that is
fairly unlikely to occur by accident.
UNRESOLVED ISSUE: Is "_-_" really worth having?
When a References header is shortened, at least three blanks SHOULD
be left between adjacent message IDs at each point where deletions
were made. Software preparing new References headers SHOULD preserve
multiple blanks in older References content.
NOTE: It's desirable to have some marker of where deletions
occurred, but the restricted syntax of the header makes this
difficult. Extra white space is not a very good marker, since it
may be deleted by software that ill-advisedly rewrites headers,
but at least it doesn't break existing software.
To repeat: followup agents SHOULD NOT shorten References headers.
NOTE: Unfortunately, reading agents and other software analyzing
References patterns have to be prepared for the worst anyway. The
worst includes random deletions and the possibility of circular
References chains (when References is misused in place of See-Also
The Control header content marks the article as a control message and
specifies the desired actions (other than the usual ones of filing
and passing on the article):
Control-content = verb *( space argument )
verb = 1*( letter / digit )
argument = 1*<ASCII printable character>
The verb indicates what action should be taken, and the argument(s)
(if any) supply details. In some cases, the body of the article may
also contain details. Section 7 describes the standard verbs. See
also the Also-Control header (Section 6.15).
NOTE: Control messages are often processed and filed rather
differently than normal articles.
NOTE: The restriction of verbs to letters and digits is new but is
consistent with existing practice and potentially simplifies
implementation by avoiding characters significant to command
interpreters. Beware that the arguments are under no such
restriction in general.
NOTE: Two other conventions for distinguishing control messages
from normal articles were formerly in use: a three-component
newsgroup name ending in ".ctl" or a subject beginning with
"cmsg " was considered to imply that the article was a control
message. These conventions are obsolete. Do not use them.
An article with a Control header MUST NOT have an Also-Control or
The Distribution header content specifies geographic or
organizational limits on an article's propagation:
Distribution-content = distribution *( dist-delim distribution )
dist-delim = ","
distribution = plain-component
A distribution is syntactically identical to a one-component
newsgroup name and must satisfy the same rules and restrictions. In
the absence of Distribution, the default distribution is "world".
NOTE: This syntax has the disadvantage of containing no white
space, making it impossible to continue a Distribution header
across several lines. Implementors of relayers and reading agents
are warned that it is intended that the successor to this Draft
will change the definition of dist delimiter to:
dist-delim = "," [ space ]
and are urged to fix their software to handle (i.e., ignore) white
space following the commas.
A relayer MUST NOT pass an article to another relayer unless
configuration information specifies transmission to that other
relayer of BOTH (a) at least one of the article's newsgroup(s), and
(b) at least one of the article's distribution(s). In effect, the
only role of distributions is to limit propagation, by preventing
transmission of articles that would have been transmitted had the
decision been based solely on newsgroups.
A posting agent might wish to present a menu of possible
distributions, or suggest a default, but normally SHOULD NOT supply a
default without giving the poster a chance to override it. A
followup agent SHOULD initially supply the same Distribution header
as found in the precursor, although the poster MAY alter this if
Despite the syntactic similarity and some historical confusion,
distributions are NOT newsgroup names. The whole point of putting a
distribution on an article is that it is DIFFERENT from the
newsgroup(s). In general, a meaningful distribution corresponds to
some sort of region of propagation: a geographical area, an
organization, or a cooperating subnet.
NOTE: Distributions have historically suffered from the completely
uncontrolled nature of their name space, the lack of feedback to
posters on incomplete propagation resulting from use of random
trash in Distribution headers, and confusion with newsgroups
(arising partly because many regions and organizations DO have
internal newsgroups with names resembling their internal
distributions). This has resulted in much garbage in Distribution
headers, notably the pointless practice of automatically supplying
the first component of the newsgroup name as a distribution (which
is MOST unlikely to restrict propagation!). Many sites have opted
to maximize propagation of such ill-formed articles by essentially
ignoring distributions. This unfortunately interferes with
legitimate uses. The situation is bad enough that distributions
must be considered largely useless except within cooperating
subnets that make an organized effort to restrain propagation of
their internal distributions.
NOTE: The distributions "world" and "local" have no standard magic
meaning (except that the former is the default distribution if
none is given). Some pieces of software do assign such meanings
The Keywords header content is one or more phrases intended to
describe some aspect of the content of the article:
Keywords-content = plain-phrase *( "," [ space ] plain-phrase )
Keywords, separated by commas, each follow the <plain-phrase> syntax
defined in Section 5.2. Encoded words in keywords MUST NOT contain
characters other than letters (of either case), digits, and the
characters "!", "*", "+", "-", "/", "=", and "_".
NOTE: Posters and posting agents are asked to take note that
keywords are separated by commas, not by white space. The
following Keywords header contains only one keyword (a rather
unlikely and improbable one):
Keywords: Thompson Ritchie Multics Linux
and should probably have been written:
Keywords: Thompson, Ritchie, Multics, Linux
This particular error is unfortunately rather widespread.
NOTE: Reading agents and archivers preparing indexes of articles
should bear in mind that user-chosen keywords are notoriously poor
for indexing purposes unless the keywords are picked from a
predefined set (which they are not in this case). Also, some
followup agents unwisely propagate the Keywords header from the
precursor into the followup by default. At least one news-based
experiment has found the contents of Keywords headers to be
completely valueless for indexing.
The Summary header content is a short phrase summarizing the
Summary-content = nonblank-text
As with the subject, no restriction is placed on the content since it
is intended solely for display to humans.
NOTE: Reading agents should be aware that the Summary header is
often used as a sort of secondary Subject header, and (if present)
its contents should perhaps be displayed when the subject is
The summary SHOULD be terse. Posters SHOULD avoid trying to cram
their entire article into the headers; even the simplest query
usually benefits from a sentence or two of elaboration and context,
and not all reading agents display all headers.
The Approved header content indicates the mailing addresses (and
possibly the full names) of the persons or entities approving the
article for posting:
Approved-content = From-content *( "," [ space ] From-content )
An Approved header is required in all postings to moderated
newsgroups; the presence or absence of this header allows a posting
agent to distinguish between articles posted by the moderator (which
are normal articles to be posted normally) and attempted
contributions by others (which should be mailed to the moderator for
approval). An Approved header is also required in certain control
messages, to reduce the probability of accidental posting of same;
see the relevant parts of Section 7.
NOTE: There is, at present, no way to authenticate Approved
headers to ensure that the claimed approval really was bestowed.
Nor is there an established mechanism for even maintaining a list
of legitimate approvers (such a list would quickly become out of
date if it had to be maintained by hand). Such mechanisms,
presumably relying on cryptographic authentication, would be a
worthwhile extension to this Draft, and experimental work in this
area is encouraged. (The problem is harder than it sounds because
news is used on many systems that do not have real-time access to
NOTE: Relayer implementors, please note well: it is the POSTING
AGENT that is authorized to distinguish between moderator postings
and attempted contributions, and to mail the latter to the
moderator. As discussed in Section 9.1, relayers MUST NOT, repeat
MUST NOT, send such mail; on receipt of an unApproved article in a
moderated newsgroup, they should discard the article, NOT
transform it into a mail message (except perhaps to a local
NOTE: [RFC1036] restricted Approved to a single From-content.
However, multiple moderation is no longer rare, and multi-
moderator Approved headers are already in use.
The Lines header content indicates the number of lines in the body of
Lines-content = 1*digit
The line count includes all body lines, including the signature (if
any) and including empty lines (if any) at the beginning or end of
the body. (The single empty separator line between the headers and
the body is not part of the body.) The "body" here is the body as
found in the posted article, AFTER all transformations such as MIME
Reading agents SHOULD NOT rely on the presence of this header, since
it is optional (and some posting agents do not supply it). They MUST
NOT rely on it being precise, since it frequently is not.
NOTE: The average line length in article bodies is surprisingly
consistent at about 40 characters, and since the line count
typically is used only for approximate judgements ("is this too
long to read quickly?"), dividing the byte count of the body by 40
gives an estimate of the body line count that is adequate for
normal use. This estimate is NOT adequate if the body has been
MIME encoded, but neither is the Lines header: at least one major
relayer will add a Lines header to an article that lacks one,
without considering the possibility of MIME encodings when
computing the line count.
NOTE: It would be better to have a Content-Size header as part of
MIME, so that body parts could have their own sizes, and so that
the units used could be appropriate to the data type (line count
is not a useful measure of the size of an encoded image, for
example). Doing this is preferable to trying to fix Lines.
UNRESOLVED ISSUE: Update on Content-Size?
Relayers SHOULD discard this header if they find it necessary to
re-encode the article in such a way that the original Lines header
would be rendered incorrect.
The Xref header content indicates where an article was filed by the
last relayer to process it:
Xref-content = relayer 1*( space location )
relayer = relayer-name
location = newsgroup-name ":" article-locator
article-locator = 1*<ASCII printable character>
The relayer's name is included so that software can determine which
relayer generated the header (and specifically, whether it really was
the one that filed the copy being examined). The locations specify
what newsgroups the article was filed under (which may differ from
those in the Newsgroups header) and where it was filed under them.
The exact form of an article locator is implementation-specific.
NOTE: Reading agents can exploit this information to avoid
presenting the same article to a reader several times. The
information is sometimes available in system databases, but having
it in the article is convenient. Relayers traditionally generate
an Xref header only if the article is cross-posted, but this is
not mandatory, and there is at least one new application
("mirroring": keeping news databases on two hosts identical) where
the header is useful in all articles.
NOTE: The traditional form of an article locator is a decimal
number, with articles in each newsgroup numbered consecutively
starting from 1. NNTP [RFC977] demands that such a model be
provided, and there may be other software that expects it, but it
seems desirable to permit flexibility for unorthodox
A relayer inserting an Xref header into an article MUST delete any
previous Xref header. A relayer that is not inserting its own Xref
header SHOULD delete any previous Xref header. A relayer MAY delete
the Xref header when passing an article on to another relayer.
NOTE: [RFC1036] specified that the Xref header was not transmitted
when an article was passed to another relayer, but the major news
implementations have never obeyed this rule, and applications like
mirroring depend on this disobedience.
A relayer MUST use the same name in Xref headers as it uses in Path
headers. Reading agents MUST ignore an Xref header containing a
relayer name that differs from the one that begins the path list.
The Organization header content is a short phrase identifying the
Organization-content = nonblank-text
This header is typically supplied by the posting agent. The
Organization content SHOULD mention geographical location (e.g., city
and country) when it is not obvious from the organization's name.
NOTE: The motive here is that the organization is often difficult
to guess from the mailing address, is not always supplied in a
signature, and can help identify the poster to the reader.
NOTE: There is no "s" in "Organization".
The Organization content is provided for identification only and does
not imply that the poster speaks for the organization or that the
article represents organization policy. Posting agents SHOULD permit
the poster to override a local default Organization header.
The Supersedes header content specifies articles to be cancelled on
arrival of this one:
Supersedes-content = message-id *( space message-id )
Supersedes is equivalent to Also-Control (Section 6.15) with an
implicit verb of "cancel" (Section 7.1).
NOTE: Supersedes is normally used where the article is an updated
version of the one(s) being cancelled.
NOTE: Although the ability to use multiple message IDs in
Supersedes is highly desirable (see Section 7.1), posters are
warned that existing implementations often do not correctly handle
more than one.
NOTE: There is no "c" in "Supersedes".
An article with a Supersedes header MUST NOT have an Also-Control or
The Also-Control header content marks the article as being a control
message IN ADDITION to being a normal news article and specifies the
Also-Control-content = Control-content
An article with an Also-Control header is filed and passed on
normally, but the content of the Also-Control header is processed as
if it were found in a Control header.
NOTE: It is sometimes desirable to piggyback control actions on a
normal article, so that the article will be filed normally but
will also be acted on as a control message. This header is
essentially a generalization of Supersedes.
NOTE: Be warned that some old relayers do not implement
An article with an Also-Control header MUST NOT have a Control or
The See-Also header content lists message IDs of articles that are
related to this one but are not its precursors:
See-Also-content = message-id *( space message-id )
See-Also resembles References, but without the restrictions imposed
on References by the followup rules.
NOTE: See-Also provides a way to group related articles, such as
the parts of a single document that had to be split across
multiple articles due to its size, or to cross-reference between
NOTE: See the discussion (in Section 6.5) on MAIL compatibility
issues of References and See-Also.
NOTE: In the specific case where it is desired to essentially make
another article PART of the current one, e.g., for annotation of
the other article, MIME's "message/external-body" convention can
be used to do so without actual inclusion. "news-message-ID" was
registered as a standard external-body access method, with a
mandatory NAME parameter giving the message ID and an optional
SITE parameter suggesting an NNTP site that might have the article
available (if it is not available locally), by IANA 22 June 1993.
UNRESOLVED ISSUE: Could the syntax be generalized to include URLs
as alternatives to message IDs? Here it makes much more sense
than in References.
The Article-Names header content indicates any special significance
the article may have in particular newsgroups:
Article-Names-content = 1*( name-clause space )
name-clause = newsgroup-name ":" article-name
article-name = letter 1*( letter / digit / "-" )
Each name clause specifies a newsgroup (which SHOULD be among those
in the Newsgroups header) and an article name local to that
newsgroup. Article names MAY be used by relayers to file the article
in special ways, or they MAY just be noted for possible special
attention by reading agents. Article names are case-sensitive.
NOTE: This header provides a way to mark special postings, such as
introductions, frequently-asked-question lists, etc., so that
reading agents have a way of finding them automatically. The
newsgroup name is specified for each article name because the
names may be newsgroup-specific; for example, many frequently-
asked-question lists are posted to "news.answers" in addition to
their "home" newsgroup, and they would not be known by the same
name(s) in both newsgroups.
The Article-Names header SHOULD be ignored unless the article also
contains an Approved header.
NOTE: This stipulation is made in anticipation of the possibility
that Approved headers will be involved in cryptographic
The presence of an Article-Names header does not necessarily imply
that the article will be retained unusually long before expiration,
or that previous article(s) with similar Article-Names headers will
be cancelled by its arrival. Posters preparing special postings
SHOULD include appropriate other headers, such as Expires and
Supersedes, to request such actions.
Different networks MAY establish different sets of article names for
the special postings they deem significant; it is preferable for
usage to be standardized within networks, although it might be
desirable for individual newsgroups to have different naming
conventions in some situations. Article names MUST be 14 characters
or less. The following names are suggested but are not mandatory:
intro Introduction to the newsgroup for newcomers.
charter Charter, rules, organization, moderation policies, etc.
background Biographies of special participants, history of the
newsgroup, notes on related newsgroups, etc.
subgroups Descriptions of sub-newsgroups under this newsgroup,
e.g., "sci.space.news" under "sci.space".
facts Information relating to the purpose of the newsgroup,
e.g., an acronym glossary in "sci.space".
references Where to get more information: books, journals, FTP
faq Answers to frequently asked questions.
menu If present, a list of all of the other article names
local to this newsgroup, with brief descriptions of their
Such articles may be divided into subsections using the MIME
"multipart/mixed" conventions. If size considerations make it
necessary to split such articles, names ending in a hyphen and a part
number are suggested; for example, a three-part frequently-asked-
questions list could have article names "faq-1", "faq-2", and
NOTE: It is somewhat premature to attempt to standardize article
names, since this is essentially a new feature with no experience
behind it. However, if reading agents are to attach special
significance to these names, some attempt at standard conventions
is imperative. This is a first attempt at providing some.
The Article-Updates header content indicates what previous articles
this one is deemed (by the poster) to update (i.e., replace):
Article-Updates-content = message-id *( space message-id )
Each message ID identifies a previous article that this one is deemed
to update. This MUST NOT cause the previous article(s) to be
cancelled or otherwise altered, unless this is implied by other
headers (e.g., Supersedes); Article-Updates is merely an advisory
that MAY be noted for special attention by reading agents.
NOTE: This header provides a way to mark articles that are only
minor updates of previous ones, containing no significant new
information and not worth reading if the previous ones have been
NOTE: If suitable conventions using MIME multipart bodies and the
"message/external-body" body-part type can be developed, a
replacing article might contain only differences between the old
text and the new text, rather than a complete new copy. This is
the motivation for not making Article-Updates also function as
Supersedes does: the replacing article might depend on the
continued presence of the replaced article.
7. Control Messages
The following sections document the currently defined control
messages. "Message" is used herein as a synonym for "article" unless
context indicates otherwise.
Posting agents are warned that since certain control messages require
article bodies in quite specific formats, signatures SHOULD NOT be
appended to such articles, and it may be wise to take greater care
than usual to avoid unintended (although perhaps well-meaning)
alterations to text supplied by the poster. Relayers MUST assume
that control messages mean what they say; they MAY be obeyed as is or
rejected, but MUST NOT be reinterpreted.
The execution of the actions requested by control messages is subject
to local administrative restrictions, which MAY deny requests or
refer them to an administrator for approval. The descriptions below
are generally phrased in terms suggesting mandatory actions, but any
or all of these MAY be subject to local administrative approval
(either as a class or case-by-case). Analogously, where the
description below specifies that a message or portion thereof is to
be ignored, this action MAY include reporting it to an administrator.
NOTE: The exact choice of local action might depend on what action
the control message requests, who it claims to come from, etc.
Relayers MUST propagate even control messages they do not understand.
In the following sections, each type of control message is defined
syntactically by defining its arguments and its body. For example,
"cancel" is defined by defining cancel-arguments and cancel-body.
The cancel message requests that one or more previous articles be
cancel-arguments = message-id *( space message-id )
cancel-body = body
The argument(s) identify the articles to be cancelled, by message ID.
The body is a comment, which software MUST ignore, and SHOULD contain
an indication of why the cancellation was requested. The cancel
message SHOULD be posted to the same newsgroup(s), with the same
distribution(s), as the article(s) it is attempting to cancel.
NOTE: Using the same newsgroups and distributions maximizes the
chances of the cancel message propagating everywhere the target
NOTE: [RFC1036] permitted only a single message-id in a cancel
message. Support for cancelling multiple articles is highly
desirable, especially for use with Supersedes (see Section 6.14).
If several revisions of an article appear in fast succession, each
using Supersedes to cancel the previous one, it is possible for a
middle revision to be destroyed by cancellation before it is
propagated onward to cancel its predecessor. Allowing each
article to cancel several predecessors greatly alleviates this
problem. (Posting agents preparing a cancel of an article that
itself cancels other articles might wish to add those articles to
the cancel-arguments.) However, posters should be aware that much
old software does not implement multiple cancellation properly and
should avoid using it when reliable cancellation is vitally
When an article (the "target article") is to be cancelled, there are
four cases of interest: the article hasn't arrived yet, it has
arrived and been filed and is available for reading, it has expired
and been archived on some less-accessible storage medium, or it has
expired and been deleted. The next few paragraphs discuss each case
in turn (in reverse order, which is convenient for the explanation).
EXPIRED AND DELETED. Take no action.
EXPIRED AND ARCHIVED. If the article is readily accessible and can
be deleted or made unreadable easily, treat as under AVAILABLE below.
Otherwise, treat as under EXPIRED AND DELETED.
NOTE: While it is desirable for archived articles to be
cancellable, this can easily involve rewriting an entire archive
volume just to get rid of one article, perhaps with manual actions
required to arrange it. It is difficult to envision a situation
so dire as to require such measures from hundreds or thousands of
administrators, or for that matter one in which widespread
compliance with such a request is likely.
AVAILABLE. Compare the mailing addresses from the From lines of the
cancel message and the target article, bearing in mind that local
parts (except for "postmaster") are case-sensitive and domains are
case-insensitive. If they do not match, either refer the issue to an
administrator for a case-by-case decision, or treat as if they
NOTE: It is generally trivial to forge articles, so nothing short
of cryptographic authentication is really adequate to ensure that
a cancel came from the original article's author. Moreover, it is
highly desirable to permit authorities other than the author to
cancel articles, to allow for cases in which the author is
unavailable, uncooperative, or malicious, and in which damage
and/or legal problems may be minimized by prompt cancellation.
Reliable authentication that would permit such administrative
cancels would be a worthwhile extension to this Draft, and
experimental work in this area is encouraged.
NOTE: Meanwhile, a simple check of addresses is useful accident
prevention and catches at least the most simple-minded forgers.
Since the intent is accident prevention rather than ironclad
security, use of the From address is appropriate, all the more so
because in the presence of gateways (especially redundant multiple
gateways), the author may not have full control over Sender
NOTE: The "refer... or treat as if they matched" rule is intended
to specifically forbid quietly ignoring cancels with mismatched
If the addresses match, then if technically possible, the relayer
MUST delete the target article completely and immediately. Failing
that, it MUST make the target article unreadable (preferably to
everyone, minimally to everyone but the administrator) and either
arrange for it to be deleted as soon as possible or notify an
administrator at once.
NOTE: To allow for events such as criminal actions, malicious
forgeries, and copyright infringements, where damage and/or legal
problems may be minimized by prompt cancellation, complete removal
is strongly preferred over merely making the target article
unreadable. The potential for malice is outweighed by the
importance of really getting rid of the target article in some
legitimate cases. (In cases of inadvertent copyright violation in
particular, the ability to quickly remedy the violation is of
considerable legal importance.) Failing that, making it
unreadable is better than nothing.
NOTE: Merely annotating the article so that readers see an
indication that the author wanted it cancelled is not acceptable.
Making the article unreadable is the minimum action.
NOTE: There have been experiments with making cancelled articles
unreadable, so that local news administrators could reverse
cancellations. In practice, administrators almost never find
cause to do so. Removal appears to be clearly preferable where
NOT ARRIVED YET. If practical, retain the cancel message until the
target article does arrive, or until there is no further possibility
of it arriving and being accepted (see Section 9.2), and then treat
as under AVAILABLE. Failing that, arrange for the target article to
be rejected and discarded if it does arrive.
NOTE: It may well be impractical to retain the control message,
given uncertainty about whether the target article will ever
arrive. Existing practice in such cases is to assume that
addresses would match and arrange the equivalent of deletion.
This is often done by making a spurious entry in a database of
already-seen message IDs (see Section 9.3), so that if the article
does arrive, it will be rejected as a duplicate.
The cancel message MUST be propagated onward in the usual fashion,
regardless of which of the four cases applied, so that the target
article will be cancelled everywhere even if cancellation and target
article follow different routes.
NOTE: [RFC1036] appeared to require stopping cancel propagation in
the NOT ARRIVED YET case, although the wording was somewhat
unclear. This appears to have been an unwise decision; there are
known cases of important cancellations (in situations of
inadvertent copyright violation, for example) achieving rather
poorer propagation than the target article. News propagation is
often a much less orderly process than the authors of [RFC1036]
apparently envisioned. Modern implementations generally propagate
the cancellation regardless.
Posting agents meant for use by ordinary posters SHOULD reject an
attempt to post a cancel message if the target article is available
and the mailing address in its From header does not match the one in
the cancel message's From header.
NOTE: This, again, is primarily accident prevention.
7.2. ihave, sendme
The ihave and sendme control messages implement a crude batched
predecessor of the NNTP [RFC977] protocol. They are largely obsolete
in the Internet but still see use in the UUCP environment, especially
for backup feeds that normally are active only when a primary feed
path has failed.
NOTE: The ihave and sendme messages defined here have ABSOLUTELY
NOTHING TO DO WITH NNTP, despite similarities of terminology.
The two messages share the same syntax:
ihave-arguments = *( message-id space ) relayer-name
sendme-arguments = ihave-arguments
ihave-body = *( message-id eol )
sendme-body = ihave-body
Message IDs MUST appear in either the arguments or the body, but not
both. Relayers SHOULD generate the form putting message IDs in the
body, but the other form MUST be supported for backward
NOTE: [RFC1036] made the relayer name optional, but difficulties
could easily ensue in determining the origin of the message, and
this option is believed to be unused nowadays. Putting the
message IDs in the body is strongly preferred over putting them in
the arguments because it lends itself much better to large numbers
of message IDs and avoids the empty-body problem mentioned in
The ihave message states that the named relayer has filed articles
with the specified message IDs, which may be of interest to the
relayer(s) receiving the ihave message. The sendme message requests
that the relayer receiving it send the articles having the specified
message IDs to the named relayer.
These control messages are normally sent essentially as point-to-
point messages, by using "to." newsgroups (see Section 5.5) that are
sent only to the relayer for which the messages are intended. The
two relayers MUST be neighbors, exchanging news directly with each
other. Each relayer advertises its new arrivals to the other using
ihave messages, and each uses sendme messages to request the articles
NOTE: Arguably these point-to-point control messages should flow
by some other protocol, e.g., mail, but administrative and
interfacing issues are simplified if the news system doesn't need
to talk to the mail system.
To reduce overhead, ihave and sendme messages SHOULD be sent
relatively infrequently and SHOULD contain substantial numbers of
message IDs. If ihave and sendme are being used to implement a
backup feed, it may be desirable to insert a delay between reception
of an ihave and generation of a sendme, so that a slightly slow
primary feed will not cause large numbers of articles to be requested
unnecessarily via sendme.
The newgroup control message requests that a new newsgroup be
newgroup-arguments = newsgroup-name [ space moderation ]
moderation = "moderated" / "unmoderated"
newgroup-body = body
/ [ body ] descriptor [ body ]
descriptor = descriptor-tag eol description-line eol
descriptor-tag = "For your newsgroups file:"
description-line = newsgroup-name space description
description = nonblank-text [ " (Moderated)" ]
The first argument names the newsgroup to be created, and the second
one (if present) indicates whether it is moderated. If there is no
second argument, the default is "unmoderated".
NOTE: Implementors are warned that there is occasional use of
other forms in the second argument. It is suggested that such
violations of this Draft, which are also violations of [RFC1036],
cause the newgroup message to be ignored. [RFC1036] was slightly
vague about how second arguments other than "moderated" were to be
treated (specifically, whether they were illegal or just ignored),
but it is thought that all existing major implementations will
handle "unmoderated" correctly, and it appears desirable to
tighten up the specs to make it possible for other forms to be
used in future.
The body is a comment, which software MUST ignore, except that if it
contains a descriptor, the description line is intended to be
suitable for addition to a list of newsgroup descriptions. The
description cannot be continued onto later lines but is not
constrained to any particular length. Moderated newsgroups have
descriptions that end with the string " (Moderated)" (note that this
string begins with a blank).
NOTE: It is unfortunate that the description line is part of the
body, rather than being supplied in a header, but this is
established practice. Newsgroup creators are cautioned that the
descriptor tag must be reproduced exactly as given above, must be
alone on a line, and that it is case-sensitive. (To reduce errors
in this regard, posting agents might wish to question or reject
newgroup messages that do not contain a descriptor.) Given the
desire for short lines, description writers should avoid content-
free phrases like "discussion of" and "news about", and stick to
defining what the newsgroup is about.
The remainder of the body SHOULD contain an explanation of the
purpose of the newsgroup and the decision to create it.
NOTE: Criteria for newsgroup creation vary widely and are outside
the scope of this Draft, but if formal procedures of one kind or
another were followed in the decision, the body should mention
this. Administrators often look for such information when
deciding whether to comply with creation/deletion requests.
A newgroup message that lacks an Approved header MUST be ignored.
NOTE: It would also be desirable to ignore a newgroup message
unless its Approved header names a person who is authorized (in
some sense) to create such a newsgroup. A cooperating subnet with
sufficiently strong coordination to maintain a correct and current
list of authorized creators might wish to do so for its internal
newsgroups. It also (or alternatively) might wish to ignore a
newgroup message for an internal newsgroup that was posted (or
cross-posted) to a non-internal newsgroup.
NOTE: As mentioned in Section 6.10, some form of (cryptographic?)
authentication of Approved headers would be highly desirable,
especially for control messages.
It would be desirable to provide some way of supplying a moderator's
address in a newgroup message for a moderated newsgroup, but this
will cause problems unless effective authentication is available, so
it is left for future work.
NOTE: This leaves news administrators stuck with the annoying
chore of arranging proper mailing of moderated-newsgroup
submissions. On Usenet, this can be simplified by exploiting a
forwarding facility that some major sites provide: they maintain
forwarding addresses, each the name of a moderated newsgroup with
all periods (".", ASCII 46) replaced by hyphens ("-", ASCII 45),
which forward mail to the current newsgroup moderators. More
advice on the subject of forwarding to moderators can be found in
the document titled "How to Construct the Mailpaths File", posted
regularly to the Usenet newsgroups news.lists, news.admin.misc,
A newgroup message naming a newsgroup that already exists is
requesting a change in the moderation status or description of the
newsgroup. The same rules apply.
The rmgroup message requests that a newsgroup be deleted:
rmgroup-arguments = newsgroup-name
rmgroup-body = body
The sole argument is the newsgroup name. The body is a comment,
which software MUST ignore; it SHOULD contain an explanation of the
decision to delete the newsgroup.
NOTE: Criteria for newsgroup deletion vary widely and are outside
the scope of this Draft, but if formal procedures of one kind or
another were followed in the decision, the body should mention
this. Administrators often look for such information when
deciding whether to comply with creation/deletion requests.
A rmgroup message that lacks an Approved header MUST be ignored.
NOTE: It would also be desirable to ignore a rmgroup message
unless its Approved header names a person who is authorized (in
some sense) to delete such a newsgroup. A cooperating subnet with
sufficiently strong coordination to maintain a correct and current
list of authorized deleters might wish to do so for its internal
newsgroups. It also (or alternatively) might wish to ignore a
rmgroup message for an internal newsgroup that was posted (or
cross-posted) to a non-internal newsgroup.
Unexpected deletion of a newsgroup being a disruptive action,
implementations are strongly advised to refer rmgroup messages to an
administrator by default, unless perhaps the message can be
determined to have originated within a cooperating subnet whose
members are considered trustworthy. Abuses have occurred.
7.5. sendsys, version, whogets
The sendsys message requests that a description of the relayer's news
feeds to other relayers be mailed to the article's reply address:
sendsys-arguments = [ relayer-name ]
sendsys-body = body
If there is an argument, relayers other than the one named by the
argument MUST NOT respond. The body is a comment, which software
MUST ignore; it SHOULD contain an explanation of the reason for the
The version message requests that the name and version of the relayer
software be mailed to the reply address:
version-body = body
There are no arguments. The body is a comment, which software MUST
ignore; it SHOULD contain an explanation of the reason for the
The whogets message requests that a description of the relayer and
its news feeds to other relayers be mailed to the article's reply
whogets-arguments = newsgroup-name [ space relayer-name ]
whogets-body = body
The first argument is the name of the "target newsgroup", specifying
the newsgroup for which propagation information is desired. This
MUST be a complete newsgroup name, not the name of a hierarchy or a
portion of a newsgroup name that is not itself the name of a
newsgroup. If there is a second argument, only the relayer named by
that argument should respond. The body is a comment, which software
MUST ignore; it SHOULD contain an explanation of the reason for the
NOTE: Whogets is intended as a replacement for sendsys (and
version) with a precisely specified reply format. Since the
syntax for specifying what newsgroups get sent to what other
relayers varies widely between different forms of relayer
software, the only practical way to standardize the reply format
is to indicate a specific newsgroup and ask where THAT newsgroup
propagates. The requirement that it be a complete newsgroup name
is intended to (largely) avoid the problem of having to answer
"yes and no" in cases where not all newsgroups in a hierarchy are
Any of these messages lacking an Approved header MUST be ignored.
Response to any of these messages SHOULD be delayed for at least
24 hours, and no response should be attempted if the message has been
cancelled in that time. Also, no response SHOULD be attempted unless
the local part of the destination address is "newsmap". News
administrators SHOULD arrange for mail to "newsmap" on their systems
to be discarded (without reply) unless legitimate use is in progress.
NOTE: Because these messages can cause many, many relayers to send
mail to one person, such messages, specifying mailing to an
innocent person's mailbox, have been forged as a half-witted
practical joke. A delay gives administrators time to notice a
fraudulent message and act (by cancelling the message, preparing
to divert the flood of mail into the bit bucket, or both).
Restriction of the destination address to "newsmap" reduces the
appeal of fraud by making it impossible to use it to harass a
normal user. (A site that does NOT discard mail to "newsmap", but
rather bounces it back, may incur higher communications costs than
if the mail had been accepted into a user's mailbox, but a
malicious forger could accomplish this anyway, by using an address
whose local part is very unlikely to be a legitimate mailbox
NOTE: [RFC1036] did not require the Approved header for these
control messages. This has been added because of the possibility
that cryptographic authentication of Approved headers will become
The body of the reply to a sendsys message SHOULD be of the form:
sendsys-reply = responder 1*sys-line
responder = "Responding-System:" space domain eol
sys-line = relayer-name ":" newsgroup-patterns
[ ":" text ] eol
newsgroup-patterns = newsgroup-name *( "," newsgroup-name )
The first line identifies the responding system, using a syntax
resembling a header (but note that it is part of the BODY).
Remaining lines indicate what newsgroups are sent to what other
systems. The syntax of newsgroup patterns is not well standardized;
the form described is common (often with newsgroup names only
partially given, denoting all names starting with a particular set of
components) but not universal. The whogets message provides a
The reply to a version message is of somewhat ill-defined form, with
a body normally consisting of a single line of text that somehow
describes the version of the relayer software. The whogets message
provides a better-defined alternative.
The body of the reply to a whogets message MUST be of the form:
whogets-reply = responder-domain responder-relayer
response-date responding-to arrived-via
responder-domain = "Responding-System:" space domain eol
responder-relayer = "Responding-Relayer:" space relayer-name eol
response-date = "Response-Date:" space date eol
responding-to = "Responding-To:" space message-id eol
arrived-via = "Arrived-Via:" path-list eol
responder-version = "Responding-Version:" space nonblank-text eol
whogets-delimiter = eol
pass-line = relayer-name [ space domain ] eol
The first six lines identify the responding relayer by its Internet
domain name (use of the ".uucp" and ".bitnet" pseudo-domains is
permissible, for registered hosts in them, but discouraged) and its
relayer name; specify the date when the reply was generated and the
message ID of the whogets message being replied to; give the path
list (from the Path header) of the whogets message (which MAY, if
absolutely necessary, be truncated to a convenient length, but MUST
contain at least the leading three relayer names); and indicate the
version of relayer software responding. Note that these lines are
part of the BODY even though their format resembles that of headers.
Despite the apparently fixed order specified by the syntax above,
they can appear in any order, but there must be exactly one of each.
After those preliminaries, and an empty line to unambiguously define
their end, the remaining lines are the relayer names (which MAY be
accompanied by the corresponding domain names, if known) of systems
to which the responding system passes the target newsgroup. Only the
names of news relayers are to be included.
NOTE: It is desirable for a reply to identify its source by both
domain name and relayer name because news propagation is governed
by the latter but location in a broader context is best determined
by the former. The date and whogets message ID should, in
principle, be present in the MAIL headers but are included in the
body for robustness in the presence of uncooperative mail systems.
The reason for the path list is discussed below. Adding version
information eliminates the need for a separate message to gather
NOTE: The limitation of pass lines to contain only names of news
relayers is meant to exclude names used within a single host (as
identifiers for mail gateways, portions of ihave/sendme
implementations, etc.), which do not actually refer to other
A relayer that is unaware of the existence of the target newsgroup
MUST NOT reply to a whogets message at all, although this MUST NOT
influence decisions on whether to pass the article on to other
NOTE: While this may result in discontinuous maps in cases where
some hosts have not honored requests for creation of a newsgroup,
it will also prevent a flood of useless responses in the event
that a whogets message intended to map a small region "leaks" out
to a larger one. The possibility of discontinuous recognition of
a newsgroup does make it important that the whogets message itself
continue to propagate (if other criteria permit). This is also
the reason for the inclusion of the whogets message's path list,
or at least the leading portion of it, in the reply: to permit
reconstruction of at least small gaps in maps.
Different networks set different rules for the legitimacy of these
messages, given that they may reveal details of organization-internal
topology that are sometimes considered proprietary.
NOTE: On Usenet, in particular, willingness to respond to these
messages is held to be a condition of network membership: the
topology of Usenet is public information. Organizations wishing
to belong to such networks while keeping their internal topology
confidential might wish to organize their internal news software
so that all articles reaching outsiders appear to be from a single
"gatekeeper" system, with the details of internal topology hidden
behind that system.
UNRESOLVED ISSUE: It might be useful to have a way to set some
sort of hop limit for these.
The checkgroups control message contains a supposedly authoritative
list of the valid newsgroups within some subset of the newsgroup name
checkgroups-body = [ invalidation ] valid-groups
invalidation = "!" plain-component
*( "," plain-component ) eol
valid-groups = 1*( description-line eol )
There are no arguments. The body lines (except possibly for an
initial invalidation) each contain a description line for a
newsgroup, as defined under the newgroup message (Section 7.3).
NOTE: Some other, ill-defined, forms of the checkgroups body were
formerly used. See Appendix A.
The checkgroups message applies to all hierarchies containing any of
the newsgroups listed in the body. The checkgroups message asserts
that the newsgroups it lists are the only newsgroups in those
hierarchies. If there is an invalidation, it asserts that the
hierarchies it names no longer contain any newsgroups.
Processing a checkgroups message MAY cause a local list of newsgroup
descriptions to be updated. It SHOULD also cause the local lists of
newsgroups (and their moderation statuses) in the mentioned
hierarchies to be checked against the message. The results of the
check MAY be used for automatic corrective action or MAY be reported
to the news administrator in some way.
NOTE: Automatically updating descriptions of existing newsgroups
is relatively safe. In the case of newsgroup additions or
deletions, simply notifying the administrator is generally the
wisest action, unless perhaps the message can be determined to
have originated within a cooperating subnet whose members are
NOTE: There is a problem with the checkgroups concept: not all
newsgroups in a hierarchy necessarily propagate to the same set of
machines. (Notably, there is a set of newsgroups known as the
"inet" newsgroups, which have relatively limited distribution but
coexist in several hierarchies with more widely distributed
newsgroups.) The advice of checkgroups should always be taken
with a grain of salt and should never be followed blindly.