This server is running leafnode, which is a dynamic NNTP proxy.
This means that it does not retrieve newsgroups unless someone is
actively reading them.
If you do an operation on a group - such as reading an article,
looking at the group table of contents or similar, then leafnode
will go and fetch articles from that group when it next updates.
Since you have read this dummy article, leafnode will retrieve
the newsgroup comp.sys.apple2.marketplace when fetchnews is run
the next time. If you'll look into this group a little later, you
will see real articles.
If you see articles in groups you do not read, that is almost
always because of cross-posting. These articles do not occupy any
more space - they are hard-linked into each newsgroup directory.
If you do not understand this, please talk to your newsmaster.
Leafnode can be found at