I agree with you that sending your H an email is not going to change him. But the purpose of standing up to to your H is not to change him, per se, but to show him you have boundaries he needs to observe or else.
He is indeed very abusive, mainly via his total disrespect and his aggressive encroachment on your boundaries. What's worse, and you're right again, he knows he's being abusive. It is all too plain to see that he wants to intimidate you. (He must have been a school-yard bully when he was growing up, 'cause that's how he acts.)
That's why we urge you to continue to stand your ground -- because anything that seems like appeasement to someone like your H will not bring you peace, but more abuse.
A temporary custody hearing should give just enough of a reality check to your H to at least get him to back off some. It will also protect you and your children more so than the nebulous --and thereby seemingly (to him) malleable-- arrangement you have now with H.
