The scandal at issue is simple. Federal law requires that federal employees use federal e-mail services when they are on the job. Hillary did not. She used a commercial service.
Why does this matter? Well, Federal law requires this to allow the government to control the content of all e-mails these employees send. In other words, the government wants to be able to monitor their communications and take the appropriate action in the event of some violation of personnel policy. Moreover, the government wants to be able to archive these communications so they can be produced in response to things like FIOA requests or Congressional subpoenas. Hillary's use of a private e-mail even for official communications and communications with other employees violated this law and frustrated these purposes. In fact, it now turns out that she destroyed a great many e-mails that should have been available for Congressional investigation and would have been if she had followed the law.
At this point, that is the only issue people are discussing regarding this scandal. Unfortunately, this makes the issue seem technical and nitpicky, meaning the scandal should have no legs.
But there is a more important reason the federal government requires employees to use government systems, and that reason actually does make this a genuine scandal... if anyone figures it out: security. Every single e-mail Hillary sent over the commercial site she used was likely monitored in some form by the provider, e.g. Google, and could very, very easily have been hacked by anyone from terrorists to enemy governments to journalists. Think about that!
Hillary has admitted that she used this commercial account exclusively and that she used it for any and all internal discussions with State Department and Obama Administration people. That means that e-mails about the movement of ambassadors, changes in security policies, the sending in of military units to defend embassies, the identities of intelligence personnel, and even things like Hillary's opinions on military actions all likely went through this easily hacked, commercially-monitored site.
Still don't see the scandal? Imagine if a group of special ops guys got killed because ISIS read about the upcoming attack in Hillary's hacked e-mail, or if Google shared some data on trade negotiations with Japan to buy a few favors from China for their operations in China. See the problem now?
What I find interesting about this scandal is that the MSM seems interested in pounding Hillary on the first issue, but won't mention the second issue at all. It's like they want to wound her, but not destroy her. Generally, scandals have no legs unless they are very visceral for the public or the powers that be have decided to eliminate the person and then use the scandal as their weapon. The first part of this alone should have no legs. Yet, the MSM seems to be jumping all over that. The second part would be visceral if it got out, but the MSM has completely refused to discuss it. I'm wondering if the plan isn't to encourage her to drop out now with the threat of finally starting to take her down for her propensity to engage in scandalous behavior, but not actually wounder her... just in case. Not sure.