Worried about networking email response rate

Hi, I wanted to ask what's the typical networking response rate at high targets (think UChi, Penn, Columbia)? I'm late to the game and sent 30 emails to alumni last week, with only one response. Lowk pretty worried about if there's something I'm doing that's wrong. I'm planning on sending out 60+ next week but that'll probably also include alumni from the school where I transferred from (a semi-target) and other random people.

Also should I say something new that's tailored to their profile in my follow-up? Or should I keep follow-ups short?

Thanks for helping!