A former co-worker of mine quit his job and he is telling me that he is going to post e-mail on his website between him and another worker who were mad at each other. I told him that this is illegal since the e-mail is company property and he isn't allowed to post this on any site. Though, I can't prove this - can anyone direct me where I can show him where he can't post such things since he sent e-mail on a company's account.
I think there are privacy concerns, but with regards to company property, I doubt so unless his employment contract has something stating such a clause. But do correct me if I am wrong.
That would be something that would have to be outlined in your company handbook. If the individual no longer has a copy, perhaps you can provide him with one or direct him to your HR department.
It also depends a bit on where you live. In Australia it would be illegal but I know that in the UK this has happened twice in the past year, the media picked it up, but there were no repercussions (legally) for sharing the emails.