I regularly used to trace emails which were virus infected to inform the source that they were infected.
That is until I did that with my sister in law, in Oz. "How do I know you are who you say you are?" she asked in response. So I 'phoned her. Given that by the time I 'phoned it was after midnight there, my brother was away and she was asleep in bed, she was not amused! She's never questioned my existence since tho'!