If you're okay with involving LLMs in this, you can use it to string them along and make them think you're falling for the scam (I assume it's a scam because I've never heard of a legitimate business using tactics like this). That way they waste their time chasing a lead that will never actually net them any money, and prevents them from scamming someone else in that time.

Don't even need an automated system for this, just paste their email into an AI and paste the phony response back.

I think of all the ways AI is being used, messing with scammers is one of the ways that's actually beneficial for society. You can self host a Deepseek instance on your own computer and it doesn't actually use that much energy.