Sorry to drag this up again, but I've noticed that, in the emails treated as phishing, the headers of at least one of the quoted messages have the email addresses shown again with "x-msg:
//30/" (with various numbers, not always 30) at the beginning.
I think it must be caused by the sender, as these are 3-way conversations and, even when quoting messages that contain these extra versions of the email addresses, the third person's mail is not treated as phishing.
It isn't a problem, as I've got used to unblocking his mail and dragging it to the appropriate folder, I'm just curious as to why it's happening.