When I was first in therapy and my poor therapist was trying to get me to see that what I thought was normal and okay really really wasn't -- I had a similar urge. It took months for me to even think about cutting him out of my life but once I felt it was possible, I wanted to do the same thing. I wanted to write out every awful thing and what consequences his selfish actions had caused for me and my future but I'd get awful angry texts from him before I even finished a rough draft so I gave up.

There's no world in which he cares.

I agree with what the others have said. Write it for you. Then find a way that'll satisfy the rage. I don't think dropping it in a mailbox will do it for you. You'll wonder did he get it, did he read it, was your voice heard, and you've got that here. We've heard you. Your support system has heard you.

He will never hear you.

So burn the letter. Rip it up. Destroy it and destroy him out of your life and keep moving forward.

That's my two cents. I wish the best for you.