how to Flag.DELETED a message with GNU NNTP

Question

I'm using GNU javamail to read NNTP messages:

public List<Message> getMessages(Newsgroup newsgroup) throws MessagingException   {
    LOG.fine("fetching.." + newsgroup);
    folder = root.getFolder(newsgroup.getNewsgroup());
    folder.open(Folder.READ_ONLY);
    List<Message> messages = Arrays.asList(folder.getMessages());
    LOG.fine("..fetched " + folder);
    return Collections.unmodifiableList(messages);
}

However, I'm having an indexing problem, in that I cannot figure out how to send only new or unread messages.

It's certainly possible to iterate the messages in the folder, parse the headers, and only return messages which have Xref values above a certain threshold. The header is like so:

Xref: dur.bounceme.net gwene.com.economist:594

However, it's a bit of hassle to do that for very large folders.

I've certainly seen that this isn't an unknown problem, and surely I'm re-inventing the wheel. Unfortunately, in this case, my wheel isn't even round because I cannot determine how trim (delete) messages on the NNTP server (in this case, Leafnode running on localhost).

Without iterating the entire folder, how can I grab messages above a certain threshold? Or, how can I delete messages from the folder, and, if they are deleted, will leafnode delete the messages?

It's as simple as:

message.setFlags(Flags.Flag.DELETED, true); ???

As an alternative I'm trying GNU Mailman.