Hillary Clinton supporters have defended her use of a private email account to conduct official State Department business by arguing that she emailed colleagues at their government addresses, ensuring that a copy of the correspondence would be retained on government servers and available to archivists. As it turns out, some aides to Hillary Clinton also used private email addresses. But even if Team Hillary's initial claim had held together, it wouldn't matter. Public records laws encompass not just correspondence with other government employees but also emails with third parties about government business.

That's why a particular email flagged by J.K. Trotter is important. Back in 2013, a hacker secured access to the private email account of Sidney Blumenthal, a staffer in Bill Clinton's White House. The hacker sent screenshots of his inbox to various news outlets, including Gawker. "According to those screenshots, Blumenthal was regularly sending Clinton what appeared to be freelance intelligence reports—including information and advice about the 2012 attacks in Benghazi, Libya—all of which clearly fell under the rubric of official State Department business," Trotter writes. "At the time, Gawker noted that Clinton’s apparent use of the non-official account likely violated federal regulations governing records retention, and sent inquiries directly to Clinton and to the White House asking if messages to the clintonemail.com address were being retained."

Gawker also "filed a FOIA request with the agency for all correspondence to date between Hillary Clinton and Sidney Blumenthal," Trotter continues, "specifically including any messages to or from the hdr22@clintonemail.com account." We now know that email address did, in fact, belong to former Secretary of State Clinton. Had she been following the rules and forwarding all email about official business to government servers, the State Department would've found the Blumenthal email. They found nothing.

"The State Department replied to our request by saying that, after an extensive search, it could find no records responsive to our request," Trotter writes. "That is not to say that they found the emails and refused to release them—it is conceivable, after all, that the State Department might have attempted to deny the release of the Clinton-Blumenthal correspondence on grounds of national security or Blumenthal’s own privacy. Instead, the State Department confirmed that it didn’t have the emails at all."

This is exactly why Clinton's behavior was unacceptable: It enabled her to conceal at least some official correspondence that the press and the public had a right to see, or at least to have acknowledged with an explanation, challengeable in court, of why the correspondence was exempt from the Freedom of Information Act.

Has she now turned over the Blumenthal correspondence to the State Department in the 50,000 pages of government related emails that she parted with earlier this year? Or is it still exclusively on the privately owned server that she controls? The answer may offer clues as to whether she really turned over all correspondence related to her government job, as her defenders have maintained. Either way, the private server will have helped her to evade at least one FOIA request. And we only know that much because a hacker stumbled on her emails. What, if anything, she deleted from her server may remain forever unknowable.