As the New York times reports:
Her expansive use of the private account was alarming to current and former National Archives and Records Administration officials and government watchdogs, who called it a serious breach.
“It is very difficult to conceive of a scenario — short of nuclear winter — where an agency would be justified in allowing its cabinet-level-head officer to solely use a private email communications channel for the conduct of government business,” said Jason R. Baron, a lawyer at Drinker Biddle and Reath who is a former director of litigation at the National Archives and Records Administration.
Under federal law, however, letters and emails written and received by federal officials, such as the secretary of state, are considered government records and are supposed to be retained so that congressional committees, historians and members of the news media can find them. There are exceptions to the law for certain classified and sensitive materials.This would be a major breach of protocol and a good way to put government information in dangerous hands - how secure are emails available to the general public, after all? - but it was a long time ago. Clinton left the State Department two whole years ago. What difference, at this point, does it make?
As the New York Times documents further:
Regulations from the National Archives and Records Administration at the time required that any emails sent or received from personal accounts be preserved as part of the agency’s records.
But Mrs. Clinton and her aides failed to do so.
Mr. Blanton said high-level officials should operate as President Obama does, emailing from a secure government account, with every record preserved for historical purposes.
“Personal emails are not secure,” he said. “Senior officials should not be using them.”See video 'Hillary Clinton May Have Broken Federal Laws: NY Times' here: