I’ve developed a bit of a form letter for IT recruiters who “cold call” me via email. I let them know about my current excellent package and how much I enjoy working in academia/non-profits. Then I let them know that what it would take to think about moving on. I close with an invitation to continue the discussion if they have anything that fits the bill.
Mostly I never hear back. Occasionally I’ll get a reply thanking me for being forthright and letting me know they’ll get back to me if they get anything I might be interested in. I haven’t gotten that third email yet.