If you respond to any Nigerian scam letters, even to tell them off, your email address gets placed on their mailing list of potential marks. To give them any response is to show them that they have a live email address that they will flood with thise fraudulent letters. For example, the Bogus Barrister blog set up their vacation response to acknowledge the tips about crime and scams. Nigerian scammers have harvested that email address and have send their "dear beloved" letters. Without ever responsing to them, the vacation response was enough to get our address added to that list.