Hillary Rodham Clinton and her aides at the State Department were acutely aware of the need to protect sensitive information when discussing international affairs over email and other forms of unsecure electronic communication, according to the latest batch of messages released by the agency from Clinton's tenure as secretary of state.

The State Department made public roughly 7,121 pages of Clinton's emails late Monday night, including 125 emails that were censored prior to their release because they contain information now deemed classified. The vast majority concerned mundane matters of daily life at any workplace: phone messages, relays of schedules and forwards of news articles. But in a few of the emails, Clinton and her aides noted the constraints of discussing sensitive subjects when working outside of the government's secure messaging systems - and the need to protect such information.

Senior adviser Alec Ross, in a February 2010 email intended for Clinton, cited frustration with "the boundaries of unclassified email" in a message about an unspecified country, which Ross referred to as "the country we discussed." The email appears to focus on civil unrest in Iran during the period preceding the Green Movement, when Iranian protesters used social media and the Internet to unsuccessfully challenge the re-election of then-President Mahmoud Ahmadinejad.

In an exchange from February 6, 2010, Clinton asks aide Huma Abedin for talking points for a call she's about to have with the newly appointed foreign minister of Ecuador. "You are congratulating him on becoming foreign minister, and purpose is to establish a personal relationship with him," Abedin replied. "Trying to get u call sheet, its classified...."

In another email from January 2010, Clinton aide Cheryl Mills responds angrily to a New York Times story based on leaked classified cables sent by Karl Eikenberry, the US ambassador to Afghanistan. "The leaking of classified material is a breach not only of trust, it is also a breach of the law," Mills wrote. Clinton also expressed frustration with the State Department's treatment of certain ordinary documents as classified.

After an aide noted the draft of innocuous remarks about the Israeli-Palestinian conflict was on the State Department's classified messaging system, she responded, "It's a public statement! Just email it." Sent a moment later, the statement merely said that US and British officials would work together to promote peace. "Well that is certainly worthy of being top secret," Clinton responded sarcastically.

All those emails conversations with Clinton took place via her private email account, highlighting the challenge the front-runner for the Democratic presidential nomination faces as she struggles to explain her decision to set-up a private email server at her New York home. She now says her decision to use a personal email account to conduct government business was a mistake.

The increasing amounts of blacked-out information from Clinton's email history as secretary of state will surely prompt additional questions about her handling of government secrets while in office and that of her most trusted advisers. The Democratic presidential front-runner now says her use of a home email server for government business was a mistake, and government inspectors have pointed to exchanges that never should have been sent via unsecured channels.

Experts in US government secrecy law see almost no possibility of criminal action against Clinton or her top aides in connection with now-classified information sent over unsecure email while she was secretary of state, based on the public evidence thus far. But the controversy over her private email server has been a distraction for her presidential campaign. Of particular concern are polls in key swing states showing that growing numbers of voters see Clinton as untrustworthy which could make her vulnerable in the general election should she win the Democratic nomination.

Government employees are instructed not to paraphrase or repeat in any form any classified material via unsecured email, which includes both the official state.gov email system and the account Clinton ran on her private server.

State Department spokesman Mark Toner said Monday none of the information censored in Monday's release was identified as classified when the emails were sent or received by Clinton, noting the redactions were made subsequently and only prior to the release of the emails under the Freedom of Information Act.

In total, the State Department has now released 13,269 pages of Clinton's emails, more than 25 per cent of the total that she turned over from her private server, Toner said. Clinton provided the department some 30,000 pages of emails she classified as work-related late last year, while deleting a similar amount from her server because she said they were solely personal in nature.

Clinton's use of a private email may have also created logistical problems communicating with State Department aides. "Well its clearly a state vs outside email issue," wrote Abedin in August 2010, after another aide reported missing some messages from Clinton. "State has been trying to figure it out. So lj is getting all your emazils cause she's on her personal account too."

Despite approving the creation of a relatively complex email system in her home, Clinton seemed puzzled by basic technology. In a July 2010 exchange, Clinton quizzed former staffer Phillippe Reines on how to charge the Apple tablet and update an application. Reines asks Clinton if she has a wireless Internet connection, and she replies: "I don't know if I have wi-fi. How do I find out?"