The State Department has refused to make public that and other emails Hillary Clinton exchanged with Barack Obama. | Getty Obama used a pseudonym in emails with Clinton, FBI documents reveal

President Barack Obama used a pseudonym in email communications with Hillary Clinton and others, according to FBI records made public Friday.

The disclosure came as the FBI released its second batch of documents from its investigation into Clinton’s private email server during her tenure as secretary of state.

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The 189 pages the bureau released includes interviews with some of Clinton’s closest aides, such as Huma Abedin and Cheryl Mills; senior State Department officials; and even Marcel Lazar, better known as the Romanian hacker “Guccifer.”

In an April 5, 2016 interview with the FBI, Abedin was shown an email exchange between Clinton and Obama, but the longtime Clinton aide did not recognize the name of the sender.

"Once informed that the sender's name is believed to be pseudonym used by the president, Abedin exclaimed: 'How is this not classified?'" the report says. "Abedin then expressed her amazement at the president's use of a pseudonym and asked if she could have a copy of the email."

The State Department has refused to make public that and other emails Clinton exchanged with Obama. Lawyers have cited the "presidential communications privilege," a variation of executive privilege, in order to withhold the messages under the Freedom of Information Act.

The report doesn't provide more details on the contents of that particular email exchange, but says it took place on June 28, 2012, and had the subject line: "Re: Congratulations." It may refer to the Supreme Court's ruling that day upholding a key portion of the Obamacare law.

A report on the FBI's June 7, 2016 interview with "Guccifer" confirms FBI Director James Comey's claim that Lazar falsely asserted that he'd surreptitiously accessed Clinton's server.

"Lazar began by stating that he had never claimed to hack the Clinton server. [An FBI agent] then advised that Fix News had recently published an article which reported that Lazar had claimed to have to Clinton server. Lazar then stated that he recalled the interview with Fox News, and that he had lied to them about hacking the Clinton server."

Additional FBI interviewees whose reports were made public Friday included Jake Sullivan, Clinton's policy planning director; Bryan Pagliano, a former Clinton technology aide; Monica Hanley, a veteran Clinton aide who worked for her in the Senate and at State; and Sidney Blumenthal, Clinton’s longtime confidant.

The so-called "302" reports also detail FBI interviews with former Secretary of State Colin Powell, former CIA acting director Mike Morell, State Department official Pat Kennedy, State Department Inspector General Steve Linick, Bill Clinton aide Justin Cooper, former diplomatic security chief Eric Boswell and longtime diplomat Lewis Lukens.

Some of the interview reports had the subject's name removed on privacy grounds before the records were released. Many of those people seem to be computer technicians or lower-level State Department officials.

The FBI published 58 pages of documents earlier this month that revealed Clinton had relied on others’ judgment to not send her classified material during email correspondences.

“Clinton did not recall receiving any emails she thought should not be on an unclassified system,” the FBI said in its Sept. 2 report. “She relied on State officials to use their judgment when emailing her and could not recall anyone raising concerns with her regarding the sensitivity of the information she received at her email address.”

