Pull out 200 of each set, or whatever number you like. Email the other 1800 and say "thanks, but we have decided not to interview you for this role. We'll keep

Pull out 200 of each set, or whatever number you like. Email the other 1800 and say "thanks, but we have decided not to interview you for this role. We'll keep your resume and contact you again if we have a role that you seem good for". Read all the remaining resumes over the next week. Seriously, it isn't complicated.