This is scam obviously. It is like a stranger who promises you a $500 by asking you to hand over your ATM card and pin.
It wouldn't cost the scammers anything to send out hundreds of thousands of those emails. They make profits if they get one person out of a hundred thousand to respond to them. It's little different to those email spam adverts that most users ignore. It only needs a tiny number of people to respond to make it worth while for a scammer/advertiser to compose an email and mass mail it.
If we make sure nobody responds to that scam email the scammer might give up because there's no reward for him.
ya but if someone owns bitcoin on blockchain.info they probably know how bitcoin works meaning they have they intellect of not giving random people their money