Darwin Magazine has an article on how email is being used by the prosecution in some high-profile court cases. The trail of email gave the prosecutors plenty of room in which to argue their cases.
Does your company have an e-mail retention policy? What does your company tell you about e-mail indiscretion? What kinds of things would you never put in an e-mail? What kinds of things would you never even joke about?
Even if there wasn't illicit intent in the original conversations, the email chains do not store enough context to prove innocence. But there is plenty of hints that one can take down the path of guilt.
Be careful what you write. And if you don't think it should be said publicly, don't say it on email.