Percy writes:
Clinton used her personal server to send and receive State Department emails, including emails containing classified information, and including to people who had insufficient clearance.
There is a bit of nuance on this point, if I understand the situation correctly.
There are files marked "Classified" (Big C). They have a specific header on them marking them as classified.
Then there is classified information (little c). This is information you have learned from files marked Classified. What Hillary apparently did in some emails is discuss this classified information with other people over her private server. As far as I know, she did not send out files marked Classified (Big C) on her private email server.
From the wiki page:
"Three emails, out of 30,000, were found to be marked as classified, although they lacked classified headers and were only marked with a small "c" in parentheses, described as "portion markings" by Comey"
So only 3 emails had any markings declaring them to be Classified at the time they were handled by Clinton's email server.
Other former Secretaries of State have also used personal email addresses, but not to the extent of Clinton, and not with as serious lapses.
That is debatable. Secretary Powell discussed classified information over AOL servers, if memory serves. This certainly doesn't excuse anyone's behavior, including Clinton's, but it does give some context.