What you need is a restraining order to stop the damaging emails and behaviour.
You can terminate parental rights, but that would end his liability for child support. Why would you want to make him that gift?
Another alternative would be to seek a restraining order against his contact with you and the child and update the child support at the same time.
This is complicated. You need an attorney to do the papers and the court appearance.
This is not confidential advice and I am not your attorney until we have had a confidenial consultation by phone or in the office.