I want to respond but then I think why? What would it get me?
Right. He is trying to HOOK you. It would get you right back to the place you are trying to get out of.
Would I be able to let it go if I just composed one thought out email and sent it and be done with it?
If you need your feelings validated, or you need closure, how about compose one thought out email and post it here. We will read it and reply in a way that a healthy person who cares about you would.
Replying to HIM is just going to get you more of the same sickness and takes the chance that you get hooked back in with him. Yuck.