Emails are hearsay evidence and there needs to be authentication before they will ever get into evidence. If the e-mail account from where the emails came was accessible to others, it is highly doubtful it would be allowed to be entered as evidence. The judge decides what form of evidence can be submitted in court and the same is true with emails.
If an e-mail can be connected to the person without there being any doubt of someone else having sent it, then it is possible it could be used as evidence. What level of connection can be established as to your ex-wife may need to be established by a forensic investigation.
Email admissibility in court can vary from state to state. And admissibilty rulings vary from courtroom to courtroom within the same county in a state, sometimes. Federal courts have differing standards, too. And, even if admissible, email evidence is sometimes easy to refute because of the ease with which an email can be sent and made to look like it is the real thing.
Hope that helps.
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