It is NOT an open relay - I have tested.
Question: How do I find out what (or from where - internal or external) the messages are originating.
At the moment I am remote, but will be heading on site shortly (have to clear the decks to get there).
I have enabled message tracking (on full logging), but can't see anything helpful.
It looks like the attack has stopped (it happened overnight) but it is the second time in a week (different emails going out).