Hillary Clinton did not have an official email address during her four years as secretary of state and used a private account to conduct government business, The New York Times reported. The practice appears to have been in violation of the Federal Records Act, which requires that official correspondence be retained.

During her tenure, Clinton's aides at the State Department took no steps to have her emails preserved on government servers. Two months ago, her advisers had to sift through tens of thousands of pages of personal messages and decide which ones to turn over to help the department comply with federal record-keeping practices; in the end, some 55,000 pages were submitted.

Jason Baron, an attorney who once served as director of litigation at the National Archives and Records Administration, said the then-secretary's communication habits were highly unusual.

"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," Baron said.

The records agency stipulates that personal email can only be used in "emergency situations," CNN detailed. In such cases, messages are to be "captured and managed in accordance with agency record-keeping practices."

Clinton spokesman Nick Merrill confirmed on Tuesday that the former top diplomat had used her personal account "when engaging with any department officials." He argued the practice was in line with that employed by Clinton's predecessors.

"For government business, she emailed them on their department accounts, with every expectation they would be retained," Merrill said. "When the Department asked former secretaries last year for help ensuring their emails were in fact retained, we immediately said yes."

Through her spokesman, Clinton – considered the frontrunner for the Democratic nomination in the 2016 White House race – insisted her communications approach was perfectly legal.

"Both the letter and spirit of the rules permitted State Department officials to use non-government email, as long as appropriate records were preserved," Merrill said.