See https://scientificspam.net/?p=329

This is something we have discussed before…

If we listed you because of the backscatter, and you write in to ask for it to be removed, and we receive a C/R so that our reply would be delivered to you…

That’s just wrong.

We won’t click on it. You won’t receive our reply, and the conversation will never proceed, and you will not be delisted. But that’s OK – the support conversation we just attempted to have with you actually proved the validity of our listing once again.

Challenge/response is spam. Stop it.