Hillary Clinton had the right to delete messages from her personal e-mail account that she deemed non-work related while she was Secretary of State, the US Department of Justice said in a court filing.
The filing came in response to legal action filed by Judicial Watch, a conservative monitoring group that wants access to all of Clinton's e-mail while she was the top US diplomat.
"There is no question that former Secretary Clinton had authority to delete personal emails without agency supervision -- she appropriately could have done so even if she were working on a government server," the Justice Department wrote in a document filed this week in US District Court in Washington.
Clinton, the front-runner for the Democratic Party presidential nominee, has been dogged for months by revelations that she used a private email account and home server in lieu of the official government email system while she was secretary of state from 2009 to 2013.
Under US National Archives State Department policies, "individual officers and employees are permitted and expected to exercise judgment to determine what constitutes a federal record," the DOJ said.
The scandal broke in March, and it wasn't until September 9 that Clinton publicly apologized for using her private e-mail server.
"That was a mistake. I'm sorry about that. I take responsibility," she said in an interview with ABC News.
"As I look back at it now, even though it was allowed, I should have used two accounts, one for personal emails, one for work-related emails," she said.
Clinton turned over 30,000 official emails to the US State Department in late 2014. The messages are being released to the public in batches.
Many contain information that has been retroactively classified -- raising questions about whether Clinton was inappropriately sending and receiving sensitive material, and whether sufficient security measures were in place to protect her private server from hackers.
FBI experts are examining the server, which Clinton eventually handed over after months of refusal, to determine whether the arrangement has compromised secret government data.
Clinton is scheduled to testify on October 22 before a Republican-led House panel investigating the deadly 2012 attack on the US mission in the Libyan city of Benghazi.
Democrats have called for the panel to be disbanded, saying it is nothing but an anti-Clinton witch hunt. But the probe goes on, and has even widened to take in the email issue.
In the Senate, two committees are also looking at Clinton's email woes, and their Republican leaders they could offer immunity to a former staffer tasked with installing the server in order to secure his testimony.