It's illegal for an official with the federal government to conduct government business on a private server.
George W. Bush's White House "lost" 22 million emails
Like Clinton, the Bush White House used a private email server—its was owned by the Republican National Committee. And the Bush administration failed to store its emails, as required by law, and then refused to comply with a congressional subpoena seeking some of those emails. “It’s about as amazing a double standard as you can get,” says Eric Boehlert,
“If you look at the Bush emails, he was a sitting president, and 95 percent of his chief advisers’ emails were on a private email system set up by the RNC.
When the Democrat-led Senate Judiciary Committee subpoenaed related emails, Bush’s attorney general, Alberto Gonzalez, said many were inaccessible or lost on a nongovernmental private server run by the RNC and called
gwb43.com. The White House, meanwhile, officially
refused to comply with the congressional subpoena.
Senate Judiciary Chairman Patrick Leahy (D-Vt.) called the president’s actions “Nixonian stonewalling” and at one point took to the floor in exasperation and shouted, “They say they have not been preserved. I don't believe that!”
the Bush White House admitted
it had lost 22 million emails, not 5 million.