First, there were never any "classified emails". A RightWing Repub Inspector General politically and retroactively reclassified a few emails with the intent to create a false scandal. Senator Feinstein, who has a high-level security clearance, read the content of the emails in question, and stated there was nothing in any of the emails that deserved even the lowest level of classification. Additionally, 'someone' leaked one of the two emails that the Inspector General had retroactively labeled as "Top Secret", and it only contained a copy of a newspaper article that was published in newspapers all over the planet.
Second, the "private server" was the server that President Clinton had setup to house the White House website and presidential materials from his terms in office. It was located at their Westchester residence surrounded and guarded by the Secret Service. Furthermore, while the State Dept, Pentagon, White House, and other top government servers had been breached and hacked, the Clinton server was never breached or hacked.
The use of the "private server" was not in violation of any federal statute or regulation, and given the State Dept server had been breached and hacked, it turned out to be quite a smart and prudent move, security-wise. To the contrary, the Chimpy Bush White House utilized private emails and private servers, in direct violation of federal law, as did Ivanka & Jared and other White House personnel in the Donnie administration.