For years (and due to a comment I read here changing my ways), I have responded to all the cold emails and linkedin messages I get from recruiters with a short polite response thanking them for their consideration and saying I will reach out if I become interested in new opportunities. So this time I actually did that last part: I reached out to a recruiter who had sent me a linkedin message a year or so earlier. He didn't actually work for the company any longer (if I'm remembering correctly), but knew the person who had taken his role. He put me in touch with her and she got me started on the interview process.