Former US Secretary of State Hillary Clinton. Reuters The FBI has been able to recover deleted emails from former Secretary of State Hillary Clinton's personal server, a source close to the investigation told Bloomberg.

And intriguingly, agents sifting through the emails Clinton said were "personal" in nature have reportedly handed some over to investigators — indicating that they are relevant in at least some way to the FBI's ongoing investigation.

"Once the emails have been extracted, a group of agents has been separating personal correspondence and passing along work-related messages to agents leading the investigation," Bloomberg reported.

Facing criticism earlier this year for exclusively using a private server during her time as secretary of state, Clinton handed over about 30,000 work-related emails for the State Department to make public. She deleted about 31,000 emails she says were personal.

At a press conference in March, Clinton claimed that the deleted correspondences had to do with yoga routines, family vacations, and plans for her daughter Chelsea's wedding.

The FBI is investigating the configuration of that server as well as whether sensitive information ever passed through her private inbox while she served as secretary of state.

It is unclear how many deleted emails the FBI has been able to find. The IT firm Clinton hired to oversee the server after she left the State Department, Platte River Networks, said last month that it was "highly likely" a backup copy of the server was made. And an official speaking to The New York Times said the emails had not been difficult to recover.

Clinton handed over her server to FBI agents in August, five months after first acknowledging that she had exclusively used a private email server to send and receive work-related emails while serving as secretary of state.

At the time, a House committee requested access to Clinton's server to ensure that she had not deleted any work-related emails. But her lawyer, David Kendall, told the committee that Clinton aides had changed the server's settings so that only emails she sent and received in the previous 60 days would be saved.

'These 2 things can't both be true'

Clinton during a speech in the gymnasium of Moulton Elementary School in Des Moines, Iowa, on Tuesday. REUTERS/Brian C. Frank

Clinton's use of the server was allowed under State Department regulations, but there are rules governing how the server should be configured and protected so it is not vulnerable to cyberattacks.

It is still unclear which safeguards were taken to protect it. And cybersecurity experts have raised the point that if Clinton's team wasn't able to delete old emails properly, then it may not have known how to properly secure the server, either.

"Clinton's private email server was secure. Clinton's people didn't know how to delete her old emails," Christopher Soghoian, a technologist for the American Civil Liberties Union, tweeted on Wednesday.

"These two things can't both be true."

'Clinton and her senior staff routinely sent foreign government information'

The FBI investigation has reportedly centered on 18 US Code 793, a section of the Espionage Act related to gathering and transmitting national-defense information, and is being led by an FBI "A-team" out of its Washington, D.C., headquarters.

"Nearly all [FBI] investigations are assigned to one of the bureau's 56 field offices," The New York Times reported last month.

"But given this inquiry's importance, senior FBI officials have opted to keep it closely held in Washington in the agency's counterintelligence section, which investigates how national security secrets are handled."

The FBI's headquarters in the J. Edgar Hoover Building in D.C. FBI.gov

Clinton has insisted she never sent or received any information marked "classified." But last month a Reuters report detailed how some of the information Clinton shared with colleagues was inherently classified, even if it was not marked as such.

"Clinton and her senior staff routinely sent foreign government information among themselves on unsecured networks several times a month, if the State Department's markings are correct," Reuters' Jonathan Allen reported.

"Within the 30 email threads reviewed by Reuters, Clinton herself sent at least 17 emails that contained this sort of information."

Anyone who inadvertently shared classified information with Clinton via email could face criminal charges and be prosecuted for "gross negligence," Bloomberg reported.

It's unknown how much classified information was consciously shared over the server. Clinton herself is not the subject of a criminal investigation, and she has since apologized for using a private server while she was at the State Department.

"That was a mistake. I'm sorry about that. I take responsibility," she said in an interview with ABC last month.