In the section on 'Logging message reception' in the Exim4 book it says
that the ID field records any Message-ID: header line, and that if
this is missing, nothing is logged but one is added before delivery.
Would it be possible to log this added Message-ID: header in the
delivery-line log for that message?
We are moving towards placing all our machines behind a NAT
firewall and it might make traceback of mail from these
machines much easier should it be necessary.
