I'd be leery of this. Once someone sends me an email, barring any prior agreement, it's mine. I may not own the ideas therein, but I certainly can claim enough

I'd be leery of this. Once someone sends me an email, barring any prior agreement, it's mine. I may not own the ideas therein, but I certainly can claim enough ownership that the sender destroying the email irrevocably, without my consent, should raise some flags. I'm seeing parallels with those useless "this email is confidential, private property, etc." footers that people stick on their emails.