We have problems in the cam.* groups with a number of posters who ignore the group's posting conventions or generally fill the groups with junk postings. Sadly the nature of Usenet (see “Cancelling Articles” in Where is cam.* hosted?) means that we can't cancel postings so you have to tackle this your end.
The solution is to use a “kill file”. This filters your postings so you only see the ones you want to see.
Most news clients include some sort of kill file system, sometimes called “message filtering” or similar. How good it will be varies a lot: some clients have little or nothing, some (e.g. Thunderbird) have some basic filtering abilities but nowhere near enough and some, especially the specialist news clients like gnus have very powerful facilities if you can work out how to use them (a basic knowledge of regular expressions tends to be a necessary skill for example).
You can find an FAQ on using kill files with the rn family of news clients here which you may find useful when writing killfile rules for your news client.
If you're reading news via Google Groups (which is a poor second best to a proper news client anyway and only recommended if your corporate firewall won't let you out on port 119) then it's trickier as Google Groups has no kill file facility. The only real solution we're aware of is to use Firefox as your web browser and then use GreaseMonkey and the Google Groups Killfile script to modify the pages Google Groups sends you.
Finally if you use leafnode then you can use that to killfile postings before they even reach your news client. In your config files you will need to set a
filterfile and, if you want to filter on Xref in your news client, you need to set
create_all_links = 1