This. Look at the email and put it into one of 2 bins: 1) A recruiter that actually read your profile in several places (Linkedin, Github, Stackoverflow) and who understood the combined picture of what they read. Send a polite canned response with an up to date "what I'm looknig for next time I switch" email.

2) Cold emails which obviously were sent to thousands with a canned message or a pitch completely foreign to your competence. Don't reply to those, you'll only get more of them and your connection to those recruiters won't have much future value either.

I get probably a dozen emails in bin 2, for every email in bin 1. Most of the bin 2 emails right now are from a company called "Data Revolution" which seems based in the UK and that I can only assume is either completely automated recruiter spam (Their profile pictures seem oddly stock-photoish), or some sort of dystopian gig-economy recruitment firm for people who rather send emails than drive Ubers.

The bin 1 contacts have actually returned on several occasions with those really rare job profiles I describe in my response, so this does work very well. I basically have a dozen people looking at job ads for me so I don't miss those one-in-a-thousand jobs I'm looking for.