First, I haven't read all the posts so far, low speed dial up so I'm not using my little bandwidth. Also a lot of this has been covered in one of the threads on HP.
First things first - a lot depends upon the laws covering the jurisdictions in which it is sent, and the laws where it's received. Whatever, the laws are, unless there is a specific law on emails, it will be covered under the general copyright laws of both locations. it's a document, the same as if written by pen on paper, and thus the IP belongs to the sender. If a corporate document, it belongs to the company.
About 10 years ago there were to landmark cases in the USA, I belive one went to their supreme court. In each case, internal emails were sent between middle level management and spoke badly about certain competitors, copies ended up in the hands of the competitors. They sued, they won and got paid damages, the courts upheld that they were valid corporate correspondence, the same as a writtne memo. In one case they found out who leaked it, and that person was sacked without notice, they sued for unfair dismissal under their states laws, they lost, the courts found that sending corporate documents to the competition was fair grounds for sacking without notice.
Many european countries, and Australia, have had cases where the courts have held that electronic documents have the same standing in law as written ones.
the use of the legalise you quote initiated in North America some years back as a response to some of those court cases. How liable you would be if you passed an email like this that was not intended for you, and you passed it to the newsmedia and they published, would be a matter for the courts to decide, at the least, they could deal with it as theft by finding. Most countries have a law that requires you hand to its lawful owner, anything that you find, if the owner can be identified, if not, you're suposed to give it to the police - lost and found.
Think of it this way, if you receive a letter from a company, that's addressed to the previous tenant of the house you rent, you have no legal right to open that letter, or to keep it, or to hand it to a third party. You can lawfully, hand it to the adressee, return it to the sender, or hand it to an authorised agent to send it on to their new address, usual the estate agent or the postal service.