I'm not quite sure what you mean by "stealing" emails. If you mean that she has been accessing your private emails without your permission, then you may be describing an invasion of privacy. Tort law generally recognizes four different types of invasion of privacy: intrusion upon seclusion; appropriation of name or picture (identity); placing the victim in a false light publicly; and private disclosure of private facts.
The law generally equates electronic mail ("email") with letters and other forms of correspondence, which are legally protected against "eavesdropping" or other unauthorized access. Depending on what your ex-wife has or hasn't done with the emails, you may have a claim for any of these types of invasions of privacy.
To have a successful tort claim, however, you need to prove not only that your privacy has been invaded, but that it has caused you some sort of harm. There is a violation of your right to seclusion and your right to privacy, which is in and of itself a harm, but one on which it is difficult to place an economic value. If your ex-wife is using the information from the emails to damage your family or business relationships, that can be another kind of harm. You should contact your state Bar association and ask for a referral to a lawyer that practices privacy rights law. Once you find a lawyer that practices in this area, you may want to contact him or her with the specific details in order to determine if you have a legitimate case.
DISCLAIMER: THIS ANSWER IS INTENDED AS INFORMATION ONLY, IT SHOULD NOT BE CONSIDERED OR RELIED ON AS FORMAL LEGAL ADVICE. ONLY AN ATTORNEY LICENSED TO PRACTICE IN YOUR JURISDICTION, AND WHO IS ACQUAINTED WITH THE RELEVANT FACTS, CAN GIVE YOU FORMAL LEGAL ADVICE.