While the State Department and National Archives took steps to recover the emails from Clinton's tenure, they did not ask the U.S. attorney general to take enforcement action. Two conservative groups filed lawsuits to force their hand.
A district judge in January ruled the suits brought by Judicial Watch and Cause of Action moot, saying State and the National Archives made a "sustained effort" to recover and preserve Clinton's records.
But Williams said the two agencies should have done more, according to the ruling in the U.S. Court of Appeals for the District of Columbia Circuit. Since the agencies neither asked the attorney general for help nor showed such enforcement action could not uncover new emails, the case was not moot.
"The Department has not explained why shaking the tree harder - e.g., by following the statutory mandate to seek action by the Attorney General - might not bear more still," Williams wrote. "Absent a showing that the requested enforcement action could not shake loose a few more emails, the case is not moot."
The State Department does not comment on pending litigation, a spokesperson said.
Williams noted that Clinton used two nongovernmental email accounts at State and continued using the Blackberry account she had while a U.S. senator during her first weeks as the nation's U.S. diplomat. She only switched to the email account hosted on her private server in March 2009, the ruling said.
"Because the complaints sought recovery of emails from all of the former Secretary's accounts, the FBI's recovery of a server that hosted only one account does not moot the suits, the judge wrote.