Ask HN: Should I respond to unsolicited recruiting emails?

As I assume many of you do, I get a number of recruiting emails from companies I've never heard of asking if I'm interested in new opportunities and so on. Some of these recruiters appear to be rather persistent - responding to the same thread up to five times without a response from me. If I'm not interested, is it customary to ignore the emails entirely or to send a short "I'm not interested right now" reply? I don't want to be rude, but writing a reply to each email would take some effort...