$750,000 is a lot of money, but seeing as some people will act on emails without signature, and that you would effectively have to invest that amount up front i

$750,000 is a lot of money, but seeing as some people will act on emails without signature, and that you would effectively have to invest that amount up front in order to attempt this attack on 15 individuals, and then hope that at least one falls for it just to make it even, I can't really see this being a viable attack vector. Maybe if the cost goes down significantly to the $100-$1000 range it might be something you would see in the wild.