Frogleg wrote in
:

My understanding is when a message is crossposted, it's only sent once
and only stored once, althougth that might be implementation dependent.
Where did you find the above quote?

http://livinginternet.com/?u/ua_cross.htm

Just one of many that seemed to answer the question gracefully.

Warning, completely non-garden technogobbleddy-goop forthcoming ...

"because it multiplies the traffic on the Internet several times without
adding any new content."

I would guess the person who wrote the article didn't have a clear
understanding of how USENET functions. He/she probably meant to imply
that crossposting unnecessarily increases the amount of articles in the
newsgroups (more 'gridlock' than 'traffic', but still not entirely
analogous) rather than the total number of bits flying across the wires.

When you post a message, your newsreader formats it to conform to a
standard listed in RFC1036 Standard for Interchange of USENET Messages.
The relevant section "2.1.3. Newsgroups" states:

***
If a message is received with a "Newsgroups" line listing some valid
newsgroups and some invalid newsgroups, a host should not remove invalid
newsgroups from the list. Instead, the invalid newsgroups should be
ignored. For example, suppose host A subscribes to the classes btl.all
and comp.all, and exchanges news messages with host B, which subscribes
to comp.all but not btl.all. Suppose A receives a message with
Newsgroups: comp.unix,btl.general.

This message is passed on to B because B receives comp.unix, but B does
not receive btl.general. A must leave the "Newsgroups" line unchanged. If
it were to remove btl.general, the edited header could eventually re-
enter the btl.all class, resulting in a message that is not shown to
users subscribing to btl.general. Also, follow-ups from outside btl.all
would not be shown to such users.
***

This would seem to imply that the message is sent only once (and not with
multiple instances for each newsgroup listed).

On the receiving end, traditionally (well in the 90s at least), a program
called 'inn' (or the daemon 'innd') receives the message. Apparently
formerly, inn would call a a program named 'crosspost'. (search for
crosspost(8) to read the 'man' page). This program is responsible for
creating 'links' to the crossposted article. On a Unix system (which was
traditionally used for serving USENET articles) files are stored as 'i-
nodes', meaning each file is simply given a number, and the filename is
associated with that number. Taking advantage of that, you can have one
file (even with differing names) listed in multiple directories (and by
extension, newsgroups) by simply recording multiple instances of the i-
node. This is called 'hard-linking'. Alternatively, you can create
'soft' or 'symbolic' links (which are analogous to Windows 'shortcuts',
but once you erase the file that the shortcut is pointing to, the link
becomes invalid. (I say formerly because apparently 'crosspost' was
obsoleted by a newer version of 'inn', but it would seem strange to
change the functionality).

All this to say, a properly crossposted article (meaning one that lists
all the newsgroups in the newsgroup line and not a message that is posted
seperately to multiple newsgroups) does not take up any significant extra
space on the server. Of course, people reading the groups still have to
deal with the same headers in multiple groups which seems to be your main
objection. I don't know of any newsreader that automatically marks read
crossposted articles as 'read', unless 'trn' does. There is a port of
'trn' for Windows, but I forgot what the name is.

Finally, according to RFC1855 Netiquette Guidelines

***
If you feel an article will be of interest to more than one Newsgroup, be
sure to CROSSPOST the article rather than individually post it to those
groups. In general, probably only five-to-six groups will have similar
enough interests to warrant this.
***

hehe, unfortunately, five seems to be the magic number. Not very
helpful, am I? *sorry* The best solution would be to find a newsreader
that manages read crossposts correctly.

Diclaimer:
I haven't worked in the industry for years, so some of the info may be
dated but should still be more or less correct.

-- Salty