They can be cross referenced with the information that's in the emails. Many have already done this. A business partner, Bobulinski, and a gmail account of one of his partners serving in prison. This is a moving story. The non-interest in even trying to verify it, as pointed out by Greenwald, is very concerning.
Most evidence can be faked. The chain of custody for evidence is important, and that's not a property of the evidence, but of its history.
There's no substitute for trust in the person or organization reporting the news.