[Exim] Adding To: headers in Exim4

Hi,

I've been using Exim3 for a while now, I upgraded to Exim4 a couple of weeks
ago, and everything is now working well, apart from one thing:

I use a mail2news gateway to pipe a few high volume mailing lists to local
groups on my leafnode nntp server. They're configured as moderated, so if I
reply, the 'newsgroup post' gets posted to the right address.

However, leafnode won't insert the To: header in the post.

This wasn't a problem with Exim3, it would create a To: header with the
correct address, and everything worked well.

Exim4 doesn't seem to do this, and I can't find an option to turn this on...

Can anyone help me?

Thanks,
Tim