[blowski]

Low response rates are used as a spam signal by major email providers, whatever the type of email.

[seba_dos1]

How does that make any sense when those are often sent from no-reply addresses that are routed nowhere?

[yakshaving_jgt]

I think response rate is meant more generally in this context. It doesn't necessarily literally mean an email in response. I think more typically it means the recipient following the call to action link in the email.