First, Hugs!! Many, many hugs!!
1. Change your email now! Why is he still able to contact you directly? No good can ever come from that.
2. DO NOT send that email! You will be the direct cause of him escalating from that content. (not that the jerk doesn't deserve it)
3. Contact your lawyer asap! Focus solely on the FACTS with the lawyer. Days, times, dates of last contact. That he blocked you when you tried to send a message from DD. That you have no way to contact him on the kids behalf.
I understand that this is very emotional for you....but the "law" will really only recognize factual information.
Please stay safe!