The person in question is clearly using their PM function to send information that is violating someone else's privacy, even if it isn't invading any privacy here on EnWorld. If the email being copied and pasted is one passed between two businesses in private, I think some of the statements in this thread regarding said email not being a matter of confidentiality are highly suspect. Third parties may not be in a legally strong position here, but EnWorld, as a private service provider (these messageboards) is in a position to use the information given them to act on their own without revealing any of that data to third parties.
It is perfectly legal for EnWorld to use their own, internal registration data to take internal action. Are they legally required to do so? Highly unlikely, unless a third party wishes to file suit against EnWorld for furnishing services that have allowed for a confidentiality breach and it can be illustrated that EnWorld took no intenal action (unlikely, but it's happened against Yahoo and similar services, which is why they are now so quick to dump yahoogroups that have allowed things like this to happen.) Does it illustrate a clear failing on EnWorld's part to have a matter such as this brought to their attention and have them state that they won't take any internal, private action despite their services being used for such activity? Yes, it most certainly does. It's like me sending a personal email (say, about my health) to a group of people I'm associated with--an email that has nothing to do with my business--and that someone creating a false account here to PM that email to other people. Regardless of whether it is illegal or not, the fact remains that something said in confidence is being spread through EnWorld's services. If EnWorld were to then tell me it wouldn't so much as take internal action (meaning they'd deal with it but couldn't tell me who was responsible), then yes, they are definately doing less than the law allows them to do and certainly less than their responsibility to their users demands. The fact that confidential business information rather than personal information is the subject of this particular instance doesn't change that.