The State Department released 5,500 pages of Hillary Clinton's personal emails from her tenure as secretary of state on the last day of 2015.

According to The Associated Press, the 2016 Democratic presidential front-runner has been under heavy criticism ever since it was revealed that she used a private and unsecured email server while she was serving under the Obama administration.

Starting in May, government officials have been releasing massive batches of Clinton's emails each month, bringing the total to more than 40,000 pages. However, the State Department fell short of reaching an order to publish 82 percent, or about 45,000 emails, by the end of the year.

"We have worked diligently to come as close to the goal as possible, but with the large number of documents involved and the holiday schedule we have not met the goal this month," the State Department said in a statement, reports USA Today. "To narrow that gap, the State Department will make another production of former Secretary Clinton's email sometime next week."

Although the former first lady claimed that she never sent or received classified information via her private email server, the latest batch of emails included 275 documents that were upgraded to "classified." Altogether 1,274 classified documents have been found in her emails.

A State Department official also told Fox News on Thursday that two of those emails were designed "secret," which is the second-highest level of classification, and most of the others were upgraded to "confidential," the lowest level of classification.

Following the release of the emails on New Year's Eve, Republican National Committee Chairman Reince Priebus issued a statement bashing the 2016 hopeful for being untrustworthy.

"With more than 1,250 emails containing classified information now uncovered, Hillary Clinton's decision to put secrecy over national security by exclusively operating off of a secret email server looks even more reckless," Priebus said Thursday night. "When this scandal first broke, Hillary Clinton assured the American people there was no classified material on her unsecure server, a claim which has since been debunked on a monthly basis with each court-ordered release."

An official with the State Department, however, explained that the classifications were retroactive.

"The information we upgraded today was not marked classified at the time the emails were sent," the official said.

The latest release includes an exchange with a State employee gushing praise over Clinton's daughter Chelsea in 2012. "Chelsea Clinton did a really great job moderating a session," the employee wrote.

John Tefft, who was the U.S. ambassador to the Ukraine at the time, also applauded Chelsea for giving a ravishing speech. "A great job cultivating a positive image of the US here. No exaggeration," he wrote.

Clinton replied to an aide who passed along the praise, saying, "As you know, hearing nice things about your children is as good as it gets. Thanks."

In another exchange, George Soros, a billionaire philanthropist who donates to liberal causes, confided to a former Clinton aide that he "regretted his decision" to support Barack Obama in the 2008 primaries over Clinton.