Can I find out who my boyfriend is talking to on craigslist?

I "accidentally" stumbled upon my boyfriend's email and lo and behold he is replying to (and posting) what I think are personal ads on craiglist (although I can't be certain from the content right now although there WERE pictures of naked girls). The only info I have on the ad are the email addresses that craigslist gives you when replying to a post in the form of Can I use this information to find out which ads he is replying to?

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