> I don't see anything wrong with attempting this.

I do, when the result of that attempt is to tell people to change their email addresses unnecessarily. Most people will fall for that.

I think most people will just think it's weird and ignore it?

The wording could obviously be better, it should use softer language with a note that if you're sure the email is correct then you can ignore the letter.

But the general concept of trying to detect unused email addresses seems valid.