I think my mail system is a little more sane now. I switched from sendmail to postfix a while back and I never had the time to get it working in the same way. I discovered at one point that I had been bouncing all email for my projectphotos domain. oops. At the time I put in a hack to make it work but now I think I have almost everything working.

All mail from my internal machines should be written to @dirk.demon.co.uk.
I found the entry that was rewriting localhost to localhost.demon.co.uk instead of dirk.demon.co.uk. It now rewrites localhost host to localhost.dirk.demon.co.uk which then gets rewritten to dirk.demon.co.uk on delivery.

Mail bounces by fetchmail now come from fetchmail@dirk.demon.co.uk instead of fetchmail@internaldomain.

The one thing I have left to do is to find a way to bounce email to users that I no nolonger wish to get mail from. Currently you would get 2 emails from fetchmail. I would prefer that postfix sends just one email.