Disclaimer: The materials provided below are informational and should not be relied upon as legal advice.
This is an invasion of your privacy and can be actionable. Do you know how this person accessed your e-mails? If they hacked into your e-mail account, you may also be able to sue them on some electronice piracy charge. You should consult your own attorney to protect your legal rights.
I disagree somewhat with counselor Mashal.
If what he has posted to his blog are the messages you actually sent, then you have little recourse. You cannot have a reasonable expectation of privacy in something you knowingly expose to public inspection, and sending him an email is no different.
The perfect defense to slander and defamation is truth. If he puports that those messages are your words and they in fact are, there is no foul.
As far as being without your knowledge, he does not have to inform you that he intends to publish your words.