In the exchange from the night of the attack, Clinton told her daughter Chelsea -- who was using the pseudonym "Diane Reynolds" -- that the attack was launched by "an Al Queda-like group."
She also expresses her grief at the loss of two American diplomats, U.S. Ambassador to Libya Chris Stevens and Sean Smith, an information management officer. Two other Americans, Tyrone Woods and Glen Doherty, died later that night after they came to the aid of diplomats at the compound.
"Very hard day and I fear more of the same tomorrow," Clinton wrote.
Rep. Jim Jordan, a member of the Select Committee on Benghazi, first brought the exchange to light last month during Clinton's marathon 11-hour testimony on the attacks.
"You tell the American people one thing," said Jordan, "you tell your family an entirely different story."
On the same night Clinton wrote the email to her daughter, she also released a public statement condemning the attack, which noted, "Some have sought to justify this vicious behavior as a response to inflammatory material posted on the Internet."
In the days and weeks that followed, the administration struggled to explain the attacks, and came under a firestorm of criticism for drawing a connection between the attack and an anti-Islam video released in the United States.
In last month's hearing, Jordan alleged that Clinton deliberately misled the American people by implying the attack erupted out of protests related to the video.
"You can live with a protest about a video," said Jordan. "That won't hurt you. But a terrorist attack will, so you can't be square with the American people. You tell your family it's a terrorist attack, but not the American people."
Republican presidential candidates have also criticized Clinton for the email, which was provided to the Benghazi committee prior to Clinton's testimony.
In a CNBC debate a few days after the hearing, Florida Sen. Marco Rubio said Clinton "admitted she had sent emails to her family saying, 'Hey, this attack at Benghazi was caused by al Qaeda-like elements.'"
"She spent over a week telling the families of those victims and the American people that it was because of a video," he said. "And yet the mainstream media is going around saying it was the greatest week in Hillary Clinton's campaign. It was the week she got exposed as a liar."
Republicans have also leveled criticism on Clinton over her use of a private email server while serving as secretary of state -- a revelation that led to this week's email release, which is part of a broader effort. The batch of emails released on Monday contained over 5,000 of Clinton's emails, about 328 of which contain information that was retroactively classified ahead of the release and therefore redacted.
Clinton has maintained that none of her emails contained information that was classified at the time she sent of received them, but an inspector general from the intelligence community flagged four emails from a 40-email sample as containing information from intelligence agencies that was classified -- two at the top secret level.
The State Department disputes that assertion.
Separately, the intelligence community's inspector general flagged another set of emails they believed contained information that should be considered classified based on the State Department's own criteria, but left it up to the State Department to make that final determination.
"ODNI and CIA classification experts judged the email as probably classified SECRET//NOFORN based on the State Department Classification Guide," Andrea Williams, a spokeswoman for the intelligence community's inspector general said in a statement Tuesday. "HOWEVER; they deferred to State Department for final adjudication. So we said from the start it's States call on classification."
Elizabeth Trudeau, a State Department spokeswoman, told reporters that one of those emails was released in Monday's batch, but the State Department ultimately did not consider it classified, and released it without upgrading its status.
That email, originally between the State Department's spokesperson and a New York Times reporter, but ultimately forwarded to Clinton, involved discussions about what the paper was planning to release from among Wikileaks-published documents.