Thunderbird since version 3 has had experimental support for junk filtering in newsgroups. The feature basically works fine, but the user interface mostly fights against your attempts to use it. I’d like to give brief instructions here for anyone who wants to try it.
You’ll need to install my addon JunQuilla to enable one critical piece of user interface. JunQuilla supports a folder property that lets you selectively enable or disable junk processing for a tree of folders. So after you’ve installed JunQuilla, enable processing of junk for a newsgroup:
This will run future posts sent to the newsgroup m.d.a.thunderbird through the bayes junk filter in Thunderbird. After this is enabled, some of the junk management controls on the folder should be enabled. Try “Run Junk Controls on Folder” to process existing posts for junk.
But nothing will appear to happen when you do, because there is no functionality to delete or hide the junk messages for newsgroups built in. Still, you can see the results using JunQuilla’s “junk percent” and “junk status +” columns:
The next step is to remove those junk messages from your view. The easiest thing to do is to create a virtual folder that shows the messages in the newsgroup without the junk messages. This is where the user interface fights against you. But you can trick it in the following manner.
Create a virtual folder on a message folder with search criteria “Junk Percent < 80”. Save the folder as a subfolder of a local mail folder. Now open the virtual folder and change the folders that it scans, removing the original folder and replacing it with the newsgroup folder:
Now the spam posts are hidden from this virtual folder:
You may need to specifically train the junk filter using a few junk and good messages in news. But the good news is that newsgroup spammers are not really optimizing against bayes filters, so it seems to be a lot easier to detect newsgroup spam than mail spam.