The more you know about the State Department, the worse Hillary's actions look

What exactly were Clinton’s aides doing that resulted in classified material being exchanged among them? Here, it helps to understand how classified information, especially highly sensitive material, is distributed within State. Some particularly sensitive intelligence is available only in hard copy. Scanning it into an unclassified email system would mean retaining the original classification markings, an exceedingly incriminating action, as explained above. Considerably more classified information is available electronically, but it cannot be transmitted from the classified to the unclassified system except by State Department technicians in very limited circumstances. For example, you cannot attach a classified document to an email on the classified system and send it to an AOL or Gmail account. One of the most fundamental protections for secure IT systems is that they are not connected to the Internet. When I was at State, for example, I had two computers behind my desk connected to completely separate classified and unclassified systems.

Given these obstacles to readily transferring classified materials into unclassified emails, what almost certainly happened is this: Clinton aides would read classified documents, either hard or electronic copies, and type the information, paraphrased or verbatim, they wanted to transmit into unclassified emails. They would then send them to Clinton, unflagged in any way as containing classified material. She could forward an email to someone else, or send it back in reply. That’s why so many emails are now redacted. If the FBI is doing its job, it will interview the senders of those emails, asking them how they obtained the information they transmitted.