If someone takes private email correspondence and, without asking permission, posts the other person's email message to a blog, what is the legal status of that content? Does the person who has not granted permission have a legal case to bring against the person who posted the content of the e-mail message?
Where are you from? If it is the US, you will have to check your states laws about that. Depending on the state it could require both parties to provide permission, or just the party that received the email, or just the party that sent the email.