No, it is forbidden from the law to profane the other people's privacy, how to read the email on other computers, messages of the mobile phones and also in this case read the private messages of the other, I am Italian and I know some laws of my country about that, there are peoples that for this paid the penalty.
With the present laws in Italy, going in tribunal if they say a*s*s*h*o*l*e to a person.
Think for the above reason, Read private Message, what happen....
I'm sorry to say, but I think you're not understanding the specifics of the Italian law. You cannot supersede in another's instrument (key point) to read their message, emails, conversations, or whatever. When users are using YOUR forum on YOUR server that law does not apply. For example you cannot use any instrument to circumvent another's person computer to read their emails there... or another server in which you do not own or lease or rent, etc. You cannot intercept cell phone conversations. So again, I'll ask where specifically does any Italian Law state what you're claiming.