In <200410182342(_dot_)45706(_dot_)blilly(_at_)erols(_dot_)com> Bruce Lilly
<blilly(_at_)erols(_dot_)com> writes:
On Mon October 18 2004 10:07, Charles Lindsey wrote:
So a Dual-Use User Agent needs some better way to determine whether the
message in hand is an email message or a news article. The proper way to
do this is to keep track of where it got it from.
A couple of typical cases are:
a) it "got it from" a flat mbox-like file or a single text message file
A file in mbox format cannot contain a news article. If the file is in
some "mbox-like" format, then it is up to the implementor of the format to
make provision.
b) it "got it from" an IMAP "folder"
There are plenty of hooks within IMAP to enable an implementor to
distinguish Email from Netnews. For example, it is customary to store news
articles in folders within a "#news" hierarchy. Messages also carry flags
with them which can be used to distinguish various classes of message.
c) it "got it from" an NNTP server after having passed through a
mail-to-news gateway
If it came from a mail-to-news gateway, then it was, by definition, a news
article.
I believe that case might apply for some people who read *this*
mailing list; N.B. this is a mailing list, not a newsgroup, and if one
insists on making a distinction, the messages sent by this list's
expander are unquestionably mail.
Indeed so. The message you are now reading has passed through a
news-to-mail gateway and is therefore, by definition, an email message.
As Ned Freed has explained to you, if there is a legitimate need to
be able to make a distinction, there is a standardized mechanism
available via RFC 3458. However I doubt that there is such a
need in the first place, and I doubt that any mechanism (including
RFC 3458) will work reliably when messages pass through gateways,
are copied to files, moved and/or copied between folders, etc.
I see nothing in RFC 3458 of relevance to this matter. It seemes to be
directed more to determining whether you are to read/listen-to/obey the
message when it arrives.
And if it was delivered via SMTP to a mail-to-news gateway, then
transported via NNTP? Or transported via NNTP to a news-to-mail
gateway, then delivered via SMTP? What if it was delivered via
UUCP? Or accessed via IMAP?
In the first case it is a news article, in the second it was a mail
message. If it arrived via UUCP, then the transport will have delivered it
either to the 'rmail' program or to the 'rnews' program. If it is in an
IMAP box, then it depends how it was put there, and that is a matter for
the IMAP implementor.
If an Agent is setting out to be for "dual-use" between two
media, then it behoves it to know which medium it is handling at any given
moment.
It's handling "messages". When a message is being transported, it
might be transported via a news-specific protocol, or via a mail-specific
protocol, or via a protocol which is non-specific. Once it has been
transported, it is simply a message.
No. Email and Netnews are distinct media. If a dual-use agent cannot keep
track of which medium it is handling, then it is broken, as is any system
which uses a non-specific protocol without suitable tagging.
And if it absolutely MUST guess which medium it is from examination of the
message, then a better discriminator would be the presence or absence of a
Return-Path header, of a "^From " line.
Return-Path fields are only inserted by SMTP when making final delivery;
Hence the presence of a Return-Path (or of an equivalent "^From " line
arising from an mbox file) is a sure sign that it is an Email. But absence
of either of those does not mean it is an email, so this mechanism is no
more than a means of guessing (fairly reliably) to be used if other
methods are not available.
--
Charles H. Lindsey ---------At Home, doing my own thing------------------------
Tel: +44 161 436 6131 Fax: +44 161 436 6133 Web: http://www.cs.man.ac.uk/~chl
Email: chl(_at_)clerew(_dot_)man(_dot_)ac(_dot_)uk Snail: 5 Clerewood Ave,
CHEADLE, SK8 3JU, U.K.
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