My name is XXXXX XXXXX I'd be happy to answer your questions today. I'm sorry to hear about your situation.
To start, what you're talking about is a misdemeanor, if she is threatening any indecent or immoral act, or using any obscene language. Code of Virginia, Section 18.2-152.7:1
Virginia also recognizes a tort for intentional interference with employment, which occurs when a person maliciously uses improper methods to try to get someone fired or other negative employment action. You have the ability to not only file suit against her for that, but to seek an injunction prohibiting her from directly or indirectly contacting your employer (so she can't have someone else forward them the emails).
Depending on the content of the emails, you can also sue for defamation of character. Defamation is any false statement that harms the reputation of the person about whom the statement is made. If the statements reflect on your ability to do your job, reputational harm is presumed. If there is a pending lawsuit, you will be able to subpeona the emails - any lawyer can issue a subpeona for documents.
There is also a tort called intentional infliction of emotional distress, which occurs when a person engages in extreme and/or outrageous conduct that serves no legitimate purpose, and is done for the purpose of causing the target to feel extreme emotional distress. You may also be able to prove that.
To start, a local attorney can help you seek an injunction against her, ordering her to stop sending the emails. He may also be able to help you get an order that she not contact you in any way, shape or form, directly or indirectly, including passing messages through your ex. A good place to look for someone is http://www.martindale.com
In the meantime, you may want to show your bosses boss' boss how to set up an email filter so that these messages do not reach his inbox and are stored in a separate folder (but saved), so he does not have to be bothered with them. The IT department can also show him how to do that, if you're not familiar with the process. It's not a complete resolution, but it would at least stop the constant stress on your employer.
If you have any questions or concerns about what I've written, please reply so that I may address them. It's important to me that you are 100% satisfied with the service I provide. Otherwise, please rate my service positively so that I get credit for answering your question. Thank you.