I would forward the emails to your case worker at the Friend of the Court and get them placed in your file. When problems arise you have a paper trail to show your attempt to cooperate in his lack thereof.
Your thinking on this subject is both rational and correct. Just ignore his demands. Just because he wants it doesn't mean you have to comply. If he violates a court order for parenting time out of spite, take him to court. Most importantly, save all emails, including the abusive ones from the new wife.
This comment is designed for general information only, and should not be construed to be formal legal advice nor the formation of a lawyer/client relationship.
You are correct. Your only obligation is to communicate with your ex regarding your son. You should save all e mails and text messages so that you have a paper trail. You should send a letter to the Friend of the Court in Genessee County detailing your situation and ask for some direction. You may want to file a motion with the Friend of the Court to schedule a hearing.
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