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Versions: 00 01

Internet Draft                                              Matt Curtin
draft-ietf-usefor-posted-mailed-01.txt        The Ohio State University
Category-to-be: Proposed standard                        Jamie Zawinski
                                                Netscape Communications

                                                              July 1998
                                    Expires: Six Months from above date


     Identification of messages delivered via both mail and news

                         Status of this Memo

This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, and
its working groups. Note that other groups may also distribute working
documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
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or to cite them other than as ``work in progress.''

To view the entire list of current Internet-Drafts, please check the
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ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast).


                               Abstract

This draft defines a format to be used when delivering a single message
to multiple destinations, where some destinations are newsgroups and
some destinations are email mailboxes.


Table of contents

1. Introduction
2. Terminology
3. Definitions of new message elements
   3.1. The Posted-And-Mailed header
   3.2. The Followup-Host header
   3.3. The message body prolog
4. Clarifications of the semantics of existing headers
   4.1. References and In-Reply-To
   4.2. Message-ID
   4.3. Followup-To
   4.4. Newsgroups
5. Security considerations
6. Acknowledgments
7. References
8. Authors' Addresses
Appendix A: Examples


1. Introduction

Most news readers include facilities for generating replies which are
either posted to news, or mailed directly to the author.  An increasing
number of news readers have the ability to do both simultaneously: to
post one copy of the message to news, and to send a copy of that same
message to a set of recipients via email.

When one receives an email message, there is currently no reliable way
to identify that message as being one which has also been posted.  This
document specifies a mechanism by which such messages may be identified.

The model used in this document is that a single message is prepared,
and then delivered on multiple transports to its various destinations.
This is not intended to dictate anything about the mechanism by which
message delivery must be implemented.  But, it is rather intended to
convey the intent that both messages should, as far as is possible, have
identical bodies and headers.

Obviously, various transports (including, but not limited to, [SMTP] and
[NNTP]) will add various headers to the messages they carry, and so it
will never be the case that two copies of the same message which are
received via different transports will be identical.  However, excepting
the headers added by the transports, it is likely that the two copies of
the message will have identical headers, and is also likely that they
will have identical bodies.

It is also recognized that certain elements of the transport
(including, but not limited to, mail-news gateways, mailing list
reflectors, and newsgroup or mailing list moderators) might modify
existing message bodies and headers.  The modification might be in
form only, such as the Content-Transfer-Encoding ([MIME]) of the body
being changed; or it might be substantive, such as a standard
disclaimer, or standard set of instructions, being appended to the
bodies.  This means that software conforming to this document cannot
guarantee that the two messages will have identical bodies by the time
they reach their destinations.  It can, however, hold that as a goal,
with the recognition that the goal will not always be reachable due to
forces beyond its control.  (In other words, the authors believe that
transport and gateway software that so alters the message bodies is
generally wrong in so doing, while recognizing that sometimes it's a
choice between evils and imperfect preservation of the message may be
the best that can be done.)


2. Terminology

In this document, we will discuss several "views" on the same logical
message.

A "combined message" is a message for which the sender has chosen some
email destinations, as well as and some news destinations.  When we are
talking about a combined message, we are either talking about it as it
appeared when composed, but before it was delivered; or we are talking
about both its mail and news aspects simultaneously.

When this document refers to a "mail message", it refers to a message
received by someone via email.  In isolation, "mail message" could refer
to either a simple mail-only message, or to the version of a combined
message that was delivered by mail.

Likewise, unless otherwise specified, "news message" refers to a message
that was received by someone via news, and that may or may not also have
been mailed.

This document assumes familiarity with the mail and news message
formats, as documented in [MAIL] and [NEWS].


3. Definitions of new message elements

3.1. The Posted-And-Mailed header

When a message is sent to both mail and news destinations, it MUST
include a Posted-And-Mailed header, with the value "yes":

  posted-and-mailed = "Posted-And-Mailed:" [CFWS] ("yes" / "no") [CFWS] CRLF

The presence of this header indicates that the message conforms to this
document.  If this header is absent, conformant software MUST assume that
the message in question DOES NOT conform to this document, and MUST NOT
treat the message as a combined message.  If this header is present but
has a value other than "yes", conformant software MUST NOT treat the
message as a combined message.

This header MUST be present both in the version of the message which was
sent to a news transport, and in the version of the message which was
sent to a mail transport, and MUST be identical in both.

This header MAY be omitted in messages which are not combined messages.
This is a reasonable thing to do, because messages which do not have
that header MUST be assumed by receiving agents to be non-combined
messages.  However, if this header is included in a non-combined
message, it MUST have the value "no".


3.2. The Followup-Host header

This header is optional.

If it is present, it is an instruction to the recipient about what news
host and protocol SHOULD be used to send a reply, should the recipient
desire to send a reply to any of the newsgroups listed in the
Followup-To or Newsgroups headers.

Background:
    It is becoming more common for discussion forums to exist which are
    for all practical purposes newsgroups, but which are served by only
    one (or a small number of) hosts.  They are not widely replicated.

    The way one uses these groups is by connecting to a particular port
    on a particular host and speaking a particular news protocol
    (typically NNTP.)

    This differs from the traditional USENET model, where one connects
    to a local news server for all activity, and the messages are
    propagated to many different hosts.

    It is not the place of this document to discuss the pros or cons of
    this mode of operation.  However, this document recognizes that this
    mode of operation exists, and defines a mechanism to deal with the
    issues related to posted-and-mailed messages as relates these
    non-USENET news hosts, as well as the more common USENET case.  It
    is noteworthy that other factors (such as Internet gateway
    architectures which prohibit connectivity between "internal"
    clients and "external" news hosts) might prevent the mechanism
    from working as desired.

The Followup-Host header SHOULD be used when all newsgroups in the
Newsgroups and Followup-To headers are served by a single, non-USENET
news server.

It MUST NOT be used when the newsgroups in question use the traditional
USENET model of propagation: that is, newsgroups which are not ones that
are served only by a particular host.

The Followup-Host header is an instruction to use a particular host for
posting activity.  Therefore, its use includes the assumption that the
recipients of the message will be able to post via the host in question.

It is recognized that even traditional USENET groups have varying levels
of propagation, and that there is no guarantee that any mail recipient
has access to any server which offers a particular USENET group.  The
Followup-Host header is not intended to address this problem.

How the posting software makes the determination of whether the current
news server is a USENET-style server, or a non-USENET style server is
unspecified.  It is left up to the implementor.  If the client cannot
make that determination, then the client MUST assume that the newsgroup
is a USENET-style one, and therefore MUST NOT include a Followup-Host
header.

One possible way to make the determination would be for software which
was able to deal with multiple news hosts to remember which hosts were
USENET and which were not.  A particular news agent might have a notion
of a "default" host, and assume that the default host was USENET, and
the non-default hosts were not.  Another news agent might ask the user
to specify whether the host carried USENET at the time the user
connected to the host (or subscribed to a group carried by it.)

The body of the Followup-Host header is a URL, as defined by [NEWSURL]:

  followup-host = "Followup-Host:" [CFWS] news-url [CFWS] CRLF

  news-url = <a URL representing a news service>

The reason for providing a full URL rather than simply a host name is
that news service may not necessarily be provided by [NNTP].  URLs,
being extensible, provide an easy way to accommodate current and future
protocol innovations.

The header's contents could be as simple as:

    Followup-Host: news://news.example.com/

indicating the default news protocol (NNTP) on the default nntp port
(TCP 119).  An NNTP service running on a nonstandard port could be
expressed as

    Followup-Host: news://news.example.com:6666/

A news service running a protocol other than NNTP would be expressed by
using a different type of URL.  For example, this header represents news
service running on the "snews" protocol (which is actually NNTP
wrapped inside of SSL):

    Followup-Host: snews://secnews.netscape.com/

It is beyond the scope of this document to document these protocols or
URL syntaxes.


3.3. The message body prolog

When a message is sent to both mail and news recipients, the posting
software MAY choose to automatically include a free-text blurb at
beginning of the message body indicating that it has been posted as well
as mailed.

If this text is inserted, it MUST be inserted in BOTH the copy of the
message that is posted, and in the copy that is mailed.  This is in
keeping with the guiding principle that two copies of the same message
MUST have the same Message-ID, and that, conversely, two messages with
the same Message-ID MUST have the same body.

Message reading software MUST NOT attempt to automatically parse or
otherwise interpret this body text.  Such software should use the
appropriate message headers instead.  This body text, like all body
text, is intended only for human consumption.

If the text is inserted, it SHOULD be kept brief: it is recommended that
it consist only of one or two lines of text.  For example,

        [[  This message was both posted and mailed.  ]]

or perhaps

        [[  This message was both posted and mailed: see
            the `To' and `Newsgroups' headers for details. ]]

But note that more verbose prologs are allowed, if desired by the user
and/or the user's software.

Rationale:
    The reason that a user or user-agent might want to insert a body
    prolog at all is to draw attention to the fact that this is a
    combined message.  Historically, mail readers did not show the
    Newsgroups header by default, and news readers did not show the To
    and CC headers by default; therefore, it is likely that, in the
    absence of the body prolog, a user might mistakenly assume that a
    combined message was mailed only, or posted only.

    The body prolog, if present, is largely redundant with the message
    headers.  This redundancy is called for due to their different uses:
    the Posted-And-Mailed header is for interpretation by programs; the
    body is for interpretation by humans.  It is intended that when
    support for the Posted-And-Mailed header becomes more widespread in
    mail and news reading software, the use of the body prolog will
    become unnecessary, and deprecated.

    There are two reasons that the same text MUST be present in both
    the mailed and posted copies, if it is present at all.

     *  The first reason is that it is a part of the message body; and
        having two different messages, with different bodies, but with
        the same Message-ID, would be a misuse of the Message-ID header.
        Therefore, if it was desired that the bodies differ, then one
        might conclude that the two different messages should have
        different Message-IDs.  However, it is HIGHLY desirable for the
        two messages to have the same ID (as discussed in section 4.2,
        "Message-ID".)  Therefore, since the two messages MUST have the
        same ID, they MUST have identical bodies.

        Some might argue that the bodies are "substantially the same",
        and that perhaps an exception should be made, and the two
        messages with non-identical bodies should be allowed to have the
        same Message-ID anyway.  The problem with this is that it is a
        slippery slope: it sets a bad precedent.  Where would it end?
        Should it be allowed for two messages to have the same ID if one
        of them is in plain-text and the other is in HTML?  If one
        includes alternate forms of attached documents?  If one has been
        spell-checked and the other has not?  If one is in English, and
        the other is a translation into Spanish?  And so on.

     *  The second reason is that the body prolog provides useful
        information to all recipients, regardless of whether they
        receive the message via news or mail.  When one sends a mail
        message To: Bob, and CC: Alice, one does not send Bob a message
        that contains only a To field, and Alice a message that contains
        only a CC field.  Rather, one discloses the full set of
        recipients to all recipients.

        The rationale for having a body prolog at all is the assumption
        that the message headers (To, CC, and Newsgroups) are not
        sufficient to fully disclose the set of recipients of the
        message, because readers will tend not to be shown those headers
        by default.

        If one accepts that the body prolog is necessary for full
        disclosure of the set of recipients to a mail recipient, then
        one must also accept that it is necessary for full disclosure to
        a news recipient.

    There is controversy over whether it is appropriate for a user agent
    to insert this text at all, the argument against it being that any
    attempt to impose structure on message bodies is both inappropriate,
    and doomed to fail.

    However, it is already the case that user agents are free to insert,
    automatically or otherwise, any manner of text into message bodies:
    for example, signature files, or "message templates."  The reason
    this document mentions the possibility of a body prolog which labels
    combined messages is simply to ensure that conformant software which
    DOES choose to insert such a blurb does so in both copies of the
    message, not just one (for the reasons enumerated above.)



4. Clarifications of the semantics of existing headers

The general principle used here is that when a header is required in
either mail or news, a combined message should include both headers.
Combined with the principle that the same message text be delivered to
both transports, this means that certain previously-news-only headers
will be delivered over mail transports, and certain previously-mail-only
headers will be delivered over news transports.

When sending a message as both mail and news, that message MUST meet the
underlying requirements of both mail messages and news messages
simultaneously.


4.1. References and In-Reply-To

Messages which are delivered to both mail and news MUST use the news
[NEWS] syntax and semantics of the References header, since that RFC has
more restrictive (and, arguably, more useful) syntax and semantics than
does the mail message standard [MAIL].

Messages which are delivered to both mail and news, and which are
replies, MUST have a References header.

If the Author-Message-ID header is present, messages sent in reply
MUST include it in the References header.

Messages which are delivered to both mail and news MAY include an
In-Reply-To header, with the semantics defined in [MAIL].  Should an
In-Reply-To header be used, it MUST contain the last message ID of the
References header (that is, the ID of the message to which this is a
reply.)


4.2. Message-ID

Messages which are delivered to both mail and news MUST have identical
Message-ID headers.

The syntax of the Message-ID header MUST be as defined in [NEWS], as
that is a more restrictive subset of the syntax defined in [MAIL].

The Message-ID header is optional in [SMTP].  Generally, if the user
agent does not generate the Message-ID, then the transport will
generate one for the message.  (This is typically true in the case of
both news and mail.  It is noteworthy that this is not a requirement
for news hosts.  Those that will behave this way go beyond the
specification.)

Since allowing the server(s) to generate the IDs would cause the use of
two different Message-IDs, in order to comply with this rule, a client
will probably need to generate the Message-ID before handing the message
to either transport.  Some suggestions for good client-side Message-ID
generation are offered in [MSGID].

(It is conceivable that some future message submission protocol might
allow the client to ask the server to generate and return a Message-ID
for it, but this is not possible with any of the currently-existing
message submission protocols.  So, the requirement is that the two
copies of the message MUST have identical Message-IDs, but any
mechanism which achieves this end is acceptable.)

Rationale:
    The requirement that the Message-IDs be identical is to make it
    possible for a recipient of a combined message to reply to it and
    generate a correct, usable References header.

    For example: if a Bob sends a combined message to a newsgroup and
    CCs the message to Alice by mail, Alice might want to reply in
    public, rather than in private: she might want to post her reply to
    the same newsgroup.  If Bob uses the same Message-ID on both, that
    works.  But, if Bob uses two different message IDs, then the message
    ID in Alice's References header will be different depending on
    whether she replies to the mailed copy or the posted copy.  If she
    replies to the mailed copy, her new news message will mention an ID
    in its References field which is not present in the newsgroup.
    Therefore, the news thread will be fractured.

    Similar fracturing effects can occur in mail, when combined messages
    are delivered to multiple mail recipients, or to newsgroups.


4.3. Followup-To

If both Posted-And-Mailed (with value "yes") and Followup-To are
present, then replies which are to be posted MUST be directed to the
newsgroups listed in the Followup-To header by default.

If a Followup-To header is present but a Posted-And-Mailed header is not
(or has a value other than "yes"), then:

  * For a news message, the proper interpretation is defined by [NEWS].

  * For a mail message, the Followup-To header MUST be ignored.


4.4. Newsgroups

If the Posted-And-Mailed header is present and has the value "yes", then
the Newsgroups header MUST also be present.  In that case, the
Newsgroups header has the semantics defined by [NEWS]: it lists the
newsgroups to which this message was posted.  This is true regardless of
whether the message in question is the mailed copy or the posted copy:
the Newsgroups header has the same semantics in both copies.

If a Newsgroups header is present but the Posted-And-Mailed header is
not, or if the Posted-And-Mailed header has some value other than "yes":

  * For a news message, the proper interpretation is defined by [NEWS].

  * For a mail message, the Newsgroups header MUST be ignored.

Rationale:
    The requirement to ignore lone Newsgroups headers in mail messages
    is an important one.  Existing practice does not allow one to make
    any assumptions about the interpretation of the Newsgroups header in
    mail, as there are two widely used, conflicting interpretations of
    it: some message-generating software uses it as an indication that
    this mail message was also posted (for example, Gnus, Pine, and
    Netscape); and some message-generating software uses it as an
    indication of the groups to which the message to which this message
    is a reply was posted (for example, rn and its direct descendants
    like trn and slrn.)

    Therefore, one MUST NOT interpret the Newsgroups header in a mail
    message unless that message is known to be in conformance with this
    document: unless there is a Posted-And-Mailed header in the message,
    the semantics of the Newsgroups header is undefined (and unsafe.)
    If there is a Posted-And-Mailed header, then the semantics of the
    Newsgroups header IS defined: by this document.


5. Security considerations

This format will reduce the risk of various unexpected results for
combined messages.  Some existing risks in email and news may stay even
with this format, but no new risks are expected as a result of using
this format.  In general, increased transportation of messages between
news and email may mean that existing risks in news are propagated to
email or the reverse, but these risks would not be reduced by the lack
of a standard for such combined messages.

The union of the security and privacy risks of existing mail and news
usage must be considered; for example, care should be taken not to
inappropriately disclose the BCC recipients of a mailed message to the
news recipients.


6. Acknowledgments

This document is derived from and inspired by earlier proposals written
by Jacob Palme and John Stanley.  Valuable feedback was provided by
Terje Bless, Stefan Haller, Lars Magne Ingebrigtsen, John Moreno, Jacob
Palme, Pete Resnick, Bart Schaefer, Jeroen Scheerder, Brad Templeton,
and Curtis Whalen.


7. References

Ref.          Author, title                         IETF status (June 1998)
                                                    ----------------------
---           -------------

[SMTP]        J. Postel: "Simple Mail Transfer      Standard, Recommended.
              Protocol", STD 10, RFC 821, August
              1982.

[MAIL]        D. Crocker: "Standard for the         Standard, Recommended.
              format of ARPA Internet text
              messages." STD 11, RFC 822, August
              1982.

[NNTP]        B. Kantor, P. Lapsley: "Network       Non-standard (but still
              News Transfer Protocol", RFC 977,     widely used as a de-facto
              February 1986.                        standard).

[NEWS]        M.R. Horton, R. Adams: "Standard      Non-standard (but still
              for interchange of USENET             widely used as a de-facto
              messages", RFC 1036, December         standard).
              1987.

[MIME]        N. Freed, N. Borenstein and           Draft Standard, elective.
              others, "Multipurpose Internet
              Mail Extensions (MIME) Part One to
              Five", RFC 2045 to 2049.

[NEWSURL]     T. Berners-Lee, L. Masinter and       Draft Standard.
              others, "Uniform Resource Locators",
              RFC 1738.

              See also:
              A. Gilman, "The 'news' URL scheme",   Internet Draft, work in
              draft-gilman-news-url-01.txt.         progress.

[USEFOR]      D. Ritter, "News Article Format",     Internet Draft, work in
              draft-ietf-usefor-article-01.txt.     progress.

[MSGID]       M. Curtin and J. Zawinski,            Internet Draft,
              "Recommendations for generating       work in progress
              Message-IDs",
              draft-ietf-usefor-message-id-01.txt.


8. Authors' Addresses

Matt Curtin
The Ohio State University
791 Dreese Laboratories
2015 Neil Ave
Columbus OH 43210
+1 614 292 7352
cmcurtin@cis.ohio-state.edu

Jamie Zawinski
Netscape Communications Corporation
501 East Middlefield Road
Mountain View, CA 94043
(650) 937-2620
jwz@netscape.com


Appendix A: Examples

The following is an example of a combined message, sent both to a
newsgroup comp.lang.c and via e-mail to a person bob@foo.example.com.

Here is the message as prepared by the message composition software:

   Date: 7 Jan 1997 12:34:21 +0000 (GMT)
   From: alice@bar.example.com
   Subject: language or grade
   Message-ID: <123zx@example.com>
   To: bob@foo.example.com
   Newsgroups: comp.lang.c
   Posted-And-Mailed: yes

   Which is it?

The same message as it might be received by someone reading it in the
newsgroup comp.lang.c:

   Path: news1.example.com!news2.example.com!bar.example.com!alice
   NNTP-Posting-Host: news2.example.com
   Xref: news.blat.example.com comp.lang.c:20465
   Lines: 1
   Date: 7 Jan 1997 12:34:21 +0000 (GMT)
   From: alice@bar.example.com
   Subject: language or grade
   Message-ID: <123zx@example.com>
   To: bob@foo.example.com
   Newsgroups: comp.lang.c
   Posted-And-Mailed: yes

   Which is it?

The same message as it might be received by a mail recipient
(presumably bob@foo.example.com):

   Return-Path: <alice@bar.example.com>
   Received: from foo.example.com [127.0.0.1] by quux.example.com
   Received: from quux.example.com [127.0.0.1] by bar.example.com
   Date: 7 Jan 1997 12:34:21 +0000 (GMT)
   From: alice@bar.example.com
   Subject: language or grade
   Message-ID: <123zx@example.com>
   To: bob@foo.example.com
   Newsgroups: comp.lang.c
   Posted-And-Mailed: yes

   Which is it?


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