Let's say the emails contain no personal or secret information, but merely state the diplomat's interpretation of his/her country's position on an issue.
It is not unusual that newspapers publish private correspondence without clearing copyright with the author. One example The Guardian: WikiLeaks embassy cables.
AFAIK, no journalist or editor has ever been convicted for copyright infringement for publishing private emails without clearing copyright first (under the rule of law – I don't know about Turkey or similar autocraties). This is a strong indication that the answer is: "Yes, a journalist can do this without infringing copyright."
However, the Church of Scientology has tried to use copyright infringement to impede free speech. The disputed materials are not emails, but the copyrighted "scriptures" that the church sell to its members e.g. Theresa A. Lyons: Scientology or censorship.
In summary: The Church of Scientology has prevailed against ex-members that have given copyrighted materials to jounalists, but journalists and newspapers that has published these materials as part of their reporting on the Church has prevailed against the Church of Scientology in these cases. The courts have found that "fair use" covers their publishing of such materials in connection with reporting.
The fact that the emails were obtained through deception would count against the journalist on the first prong of a fair use analysis, i.e. the nature of the copying. Bad faith copying was part of the problem in Gerald Ford memoir case, whose name escapes me at the moment.
But I'd still expect that fact to be outweighed by the other factors. News reporting is transformative and presumptively a fair use.
Also worth considering is the question of whether the documents are protected in the first place. The United States doesn't allow copyright protection for federal government records, but I imagine there's plenty of variation among other countries.
Almost surely yes. An assertion of copyright would be trumped by free speech considerations in that context.
A stronger legal theory for the diplomat might be a request for a gag order as a remedy for information obtained by fraud, but given the strong protections against prior restraint in the United States, this probably wouldn't be a successful claim in the United States, although it might prevail in some other countries.
Most likely yes, depending on multiple factors.
According to the U.S. Copyright Office:
Copyright, a form of intellectual property law, protects original works of authorship including literary, dramatic, musical, and artistic works, such as poetry, novels, movies, songs, computer software, and architecture. Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed.
Emailed content that meets those conditions will be protected by copyright as soon as it is written.
In the United States, an entity whose copyright is infringed can go to federal court for a variety of remedies, mostly financial. (A federal prosecutor could also pursue criminal charges.) I say "entity," because the copyright holder can be the employer who paid for the creation of the work, rather than the individual who produced it.
However, fair use is one of the exceptions to copyright infringement.
To determine whether a use is fair, a court considers four factors.
The first is the purpose and character of the use (chiefly whether it’s for criticism, comment, news reporting, teaching, or research, all of which favor fair use). The second is the nature of the copyrighted work itself (whether, say, it was unpublished, which is entitled to greater protection). The third is the amount and substantiality of the portion used in relation to the work as a whole (the more of the original work used, the more likely it’s an infringement). And the fourth is the effect of the use on the market for, or value of, the copyrighted work (uses that supplant the original work in the marketplace are unlikely to be fair).
No single factor is determinative, and notably the fact that something is newsworthy, or used in a news report, does not automatically make its use fair. That’s probably where I spend the most time educating people. Using a copyrighted work for a news report will be considered as part of factor one, but that does not end the analysis—the court will go on to consider the other factors, and if they don’t favor fair use, then your use won’t be protected.
Note the factors involved in this hypothetical case:
- The purpose and character of the use, in this case news reporting, which is a plus.
- The unpublished nature of the work, which weighs against fair use.
- The amount of the email republished.
- The value of the material in question to the market, which seems minimal if the material was not destined for publication.
The deceptive circumstances of the acquisition of the email wouldn't necessarily apply, though the details may go toward the credibility of the recipient in the eyes of the court.