How are 7-year old emails from an ex-con convincing? The only "authority" that thinks they are convincing are some editors on BusinessWeek and Reuters.
The convincing authority is the plaintiff's law firm, which has tasked their digital forensics team with analyzing the documents and concluded that it is authentic and has taken the case on. It's not just BusinessWeek and Reuters.
Have you read them? I'm not denying that it's easy to fake emails, but if you really pay attention to how the emails are written and how natural the flow of conversation between them is then you can see why they're convincing.
Con-men get pretty good at being convincing. It's something of a job requirement.
Not sure what you found convincing - it certainly screamed doctored conversation to me...