WASHINGTON (AP) -- Even if Hillary Rodham Clinton's use of a private email server to conduct official business as secretary of state was not illegal, it violated Obama administration guidance and undermined his pledge of historic transparency.

Clinton's reliance on hdr22@clintonemail.com for electronic communication as the nation's top diplomat ignited another political controversy for the presumptive Democratic presidential front-runner, who is no stranger to scandal. It was a puzzling and risky decision for a political figure who is vulnerable to criticism about trying to operate outside the rules.

Clinton has yet to explain why she took the unusual step of using her own server and eschewing a State Department email address. Her silence has left the White House that vowed to run the most open government in history in the awkward position of having to answer for her electronic secrecy.

For the second day in a row Wednesday, Clinton's emails dominated the White House press briefing. Press secretary Josh Earnest carefully avoided direct criticism of Clinton while making it clear that administration policy is for government emails to be used for official business.

30 PHOTOS Hillary Clinton -- last updated 10/10/2014 See Gallery Clinton email policy violated Obama administration guidance INDIANOLA, IA - SEPTEMBER 14: Former Secretary of State Hillary Rodham Clinton speaks to a large gathering at the 37th Harkin Steak Fry, September 14, 2014 in Indianola, Iowa. This is the last year for the high-profile political event as Sen. Tom Harkin (D-IA) plans to retire. (Photo by Steve Pope/Getty Images) INDIANOLA, IA - SEPTEMBER 14: Former President Bill Clinton speaks to a large gathering at the 37th Harkin Steak Fry, September 14, 2014 in Indianola, Iowa. This is the last year for the high-profile political event as Sen. Tom Harkin (D-IA) plans to retire. (Photo by Steve Pope/Getty Images) INDIANOLA, IA - SEPTEMBER 14: Former President Bill Clinton and his wife former Secretary of State Hillary Rodham Clinton attend the 37th Harkin Steak Fry, September 14, 2014 in Indianola, Iowa. This is the last year for the high-profile political event as Sen. Tom Harkin (D-IA) plans to retire. (Photo by Steve Pope/Getty Images) INDIANOLA, IA - SEPTEMBER 14: Former Secretary of State Hillary Rodham Clinton and U.S. Sen. Tom Harkin (D-IA) greet the crowd as they arrive onstage at the 37th Harkin Steak Fry, September 14, 2014 in Indianola, Iowa. This is the last year for the high-profile political event as Sen. Tom Harkin (D-IA) plans to retire. (Photo by Steve Pope/Getty Images) INDIANOLA, IA - SEPTEMBER 14: Former President Bill Clinton and his wife former Secretary of State Hillary Rodham Clinton attend the 37th Harkin Steak Fry, September 14, 2014 in Indianola, Iowa. This is the last year for the high-profile political event as Sen. Tom Harkin (D-IA) plans to retire. (Photo by Steve Pope/Getty Images) INDIANOLA, IA - SEPTEMBER 14: Former President Bill Clinton and his wife former Secretary of State Hillary Rodham Clinton along with U.S. Sen. Tom Harkin (D-IA) and a host of Democrats on the 2014 ballot, greet the crown at the 37th Harkin Steak Fry, September 14, 2014 in Indianola, Iowa. This is the last year for the high-profile political event as Sen. Tom Harkin (D-IA) plans to retire. (Photo by Steve Pope/Getty Images) INDIANOLA, IA - SEPTEMBER 14: Former Secretary of State Hillary Rodham Clinton speaks to a large gathering at the 37th Harkin Steak Fry, September 14, 2014 in Indianola, Iowa. This is the last year for the high-profile political event as Sen. Tom Harkin (D-IA) plans to retire. (Photo by Steve Pope/Getty Images) INDIANOLA, IA - SEPTEMBER 14: Former President Bill Clinton and his wife former Secretary of State Hillary Rodham Clinton and Ruth Harkin share a light moment during the 37th Harkin Steak Fry, September 14, 2014 in Indianola, Iowa. This is the last year for the high-profile political event as Sen. Tom Harkin (D-IA) plans to retire. (Photo by Steve Pope/Getty Images) EAST HAMPTON, NY - AUGUST 16: Hillary Rodham Clinton signs copies of her book 'Hard Choices' at BookHampton on August 16, 2014 in East Hampton, New York. (Photo by Sonia Moskowitz/Getty Images) EAST HAMPTON, NY - AUGUST 16: Hillary Rodham Clinton signs copies of her book 'Hard Choices' at BookHampton on August 16, 2014 in East Hampton, New York. (Photo by Sonia Moskowitz/Getty Images) Former US Secretary of State Hillary Clinton arrives to sign her book 'Hards Choices' at the Bunch of Grapes bookstore on Martha's Vineyard on August 13, 2014. Clinton on August 12 denied attacking US President Barack Obama over his foreign policy in Syria and Iraq, insisting she was looking forward to 'hugging it out' with the US leader when they meet at a party later this week. AFP PHOTO/Nicholas KAMM (Photo credit should read NICHOLAS KAMM/AFP/Getty Images) OAKLAND, CA - JULY 23: Former Secretary of State Hillary Clinton speaks during a during a round table event to launch the 'Talking is Teaching: Talk Read Sing' campaign at the Children's Hospital Oakland Research Institute on July 23, 2014 in Oakland, California. Former Secretary of State Hillary Clinton launched the 'Talking is Teaching; Talk Read Sing' campaign in partnership withToo Small to Fail and the Bill, Hillary and Chelsea Foundation that encourages parents and caregivers to close the word gap by talking, singing and reading to children every day from the birth. (Photo by Justin Sullivan/Getty Images) US Secretary of State Hillary Clinton (L) and US President barack Obama (R) are greeted by Myanmar pro-democracy leader Aung San Suu Kyi (C) at her residence in Yangon on November 19, 2012 . Obama arrived in Myanmar for a historic visit aimed at encouraging a string of dramatic political reforms in the former pariah state. AFP PHOTO / Nicolas ASFOURI (Photo credit should read NICOLAS ASFOURI/AFP/Getty Images) US Secretary of State Hillary Clinton (L) looks on as US President Barack Obama (2nd L) speaks during a bilateral meeting with Japanese Prime Minister Yoshihiko Noda (2nd R) on the sidelines of the East Asian Summit at the Peace Palace in Phnom Penh on November 20, 2012. During the two-day East Asia Summit in Phnom Penh, Obama was scheduled to hold talks with the leaders of the 10-member Association of Southeast Asian Nations (ASEAN) along with Chinese Premier Wen Jiabao and Japan's Yoshihiko Noda. AFP PHOTO / Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images) US President Barack Obama and Secretary of State Hillary Clinton board Air Force One at the airport in Yangon on November 19, 2012. Huge crowds greeted Barack Obama in Myanmar on the first visit by a serving US president to the former pariah state to encourage a string of startling political reforms. AFP PHOTO/Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images) BERLIN, GERMANY - JULY 06: Hillary Rodham Clinton, former United States Secretary of State, U.S. Senator, and First Lady of the United States, speaks during the presentation of the German translation of her book 'Hard Choices' ('Entscheidungen' in German) at the Staatsoper in the Schiller Theater on July 6, 2014 in Berlin, Germany. (Photo by Adam Berry/Getty Images) BERLIN, GERMANY - JULY 06: Copies of the German translation of the book 'Hard Choices' ('Entscheidungen' in German) by Hillary Rodham Clinton, former United States Secretary of State, U.S. Senator, and First Lady of the United States, stand on display at the Staatsoper in the Schiller Theater on July 6, 2014 in Berlin, Germany. (Photo by Adam Berry/Getty Images) US President Barack Obama(2nd-L), First Lady Michelle Obama(L) along with former president Bill Clinton(3rd-L) and former secretary of state Hillary Clinton(4th-L) take part in a wreath-laying ceremony in honour of the late 35th president of the US John F. Kennedy at Kennedy's gravesite in Arlington National Cemetery on November 20, 2013 in Arlington, Virginia. AFP PHOTO/Mandel NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) Commenting on the size of the drinks at Arthur Bryant's Barbecue restaurant, President Barrack Obama (middle), prepared to sit down to talk and eat with Victor Fugate (left), Mark Turner, and Becky Forrest (right) during a visit to Kansas City on Tuesday, July 29, 2014, in Kansas City, Mo. (Shane Keyser/Kansas City Star/MCT via Getty Images) AUSTIN, TX - JUNE 20: Hillary Rodham Clinton appears on stage during 'A Conversation With Former Secretary of State Hillary Rodham Clinton' at the Long Center on June 20, 2014 in Austin, Texas. (Photo by Gary Miller/Getty Images) KUALA LUMPUR, MALAYSIA - APRIL 27: U.S. President Barack Obama delivers a speech during a townhall session with the Young Southeast Asian Leadership Initiative (YSEALI) at Universiti Malaya on April 27, 2014 in Kuala Lumpur, Malaysia. The U.S. President is on an Asian tour where he is due to visit Japan, South Korea, Malaysia and Philippines. (Photo by Rahman Roslan/Getty Images) AUSTIN, TX - JUNE 20: Hillary Rodham Clinton appears on stage during 'A Conversation With Former Secretary of State Hillary Rodham Clinton' at the Long Center on June 20, 2014 in Austin, Texas. (Photo by Gary Miller/Getty Images) AUSTIN, TX - JUNE 20: Hillary Rodham Clinton appears on stage during 'A Conversation With Former Secretary of State Hillary Rodham Clinton' at the Long Center on June 20, 2014 in Austin, Texas. (Photo by Gary Miller/Getty Images) BERLIN, GERMANY - JULY 06: Hillary Rodham Clinton, former United States Secretary of State, U.S. Senator, and First Lady of the United States (R), speaks next to Christoph Amend, editor in chief of Zeit Magazin, during the presentation of the German translation of her book 'Hard Choices' ('Entscheidungen' in German) at the Staatsoper in the Schiller Theater on July 6, 2014 in Berlin, Germany. (Photo by Adam Berry/Getty Images) WASHINGTON, DC - JUNE 27: (L-R) First lady Michelle Obama, daughter Sasha Obama and U.S. President Barack Obama attend the Marine Barracks Evening Parade on June 27, 2014 in Washington, DC. The Marine Barracks Evening Parade is a tradition held in Washington and is in it's 57th year. (Photo by Kristoffer Tripplaar-Pool/Getty Images) WASHINGTON, DC - JUNE 27: (L-R) First lady Michelle Obama, daughter Sasha Obama and U.S. President Barack Obama attend the Marine Barracks Evening Parade on June 27, 2014 in Washington, DC. The Marine Barracks Evening Parade is a tradition held in Washington and is in it's 57th year. (Photo by Kristoffer Tripplaar-Pool/Getty Images) Former Secretary of State Hillary Clinton waits to speak at the World Bank May 14, 2014 in Washington, DC. Former Secretary of State Hilary Clinton and World Bank President Jim Yong Kim joined others to speak about women's rights. AFP PHOTO/Brendan SMIALOWSKI (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images) U.S. President Barack Obama, right, walks with Hillary Clinton, U.S. secretary of state, left, and Derek Mitchell, U.S. ambassador to Myanmar, after arriving at Yangon International Airport in Yangon, Myanmar, on Monday, Nov. 19, 2012. Obama hailed Myanmar's shift to democracy and urged more steps to increase freedom in the first visit to the former military regime by a U.S. president. Photographer: Dario Pignatelli/Bloomberg via Getty Images US Secretary of State Hillary Clinton (L) gestures as US President Barack Obama (2nd R) finishes a meeting with Myanmar's President Thein Sein (R) at the regional parliament building in Yangon on November 19, 2012. Obama met Myanmar's reformist leader Thein Sein during a landmark visit to Yangon aimed at encouraging political reforms. AFP PHOTO / Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images) US President Barack Obama (L) and Thai Prime Minister Yingluck Shinawatra (2nd L) walk past US representatives including US Secretary of State Hillary Clinton (R) during a welcoming ceremony at Government House in Bangkok on November 18, 2012. President Barack Obama arrived in Asia on November 18 to intensify a US foreign policy pivot towards the fast-rising region on his first overseas trip since re-election, including a landmark visit to Myanmar. AFP PHOTO/Christophe ARCHAMBAULT (Photo credit should read CHRISTOPHE ARCHAMBAULT/AFP/Getty Images) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

"Very specific guidance has been given to agencies all across the government, which is specifically that employees of the Obama administration should use their official email accounts when they're conducting official government business," Earnest said. He added if there are occasions when personal email is used for government business, a copy should be sent to the government account so the message can be properly preserved for inquiries from the public, historians and Congress.

Yet Clinton wasn't using personal email on occasion, but exclusively, the New York Times reported this week. The Associated Press found that a business record used for her email server registered under the home address for her residence in Chappaqua, New York, as early as August 2010 under the name Eric Hoteham. That name doesn't appear in public records databases, but Clinton once employed an aide named Eric Hothem, who was not available for comment Wednesday.

President Barack Obama didn't sign a law requiring archiving of emails from government officials until last year, after Clinton left office. But in 2011, when she was still secretary amid Google's revelations that China tapped email accounts of U.S. officials, the White House said government officials should use government email accounts for official business.

"The administration policy that is effective here is that we - all of our work is conducted on work email accounts," said then-press secretary Jay Carney.

Last year, Clinton provided the State Department 55,000 pages of emails after the department asked her and other former secretaries for records that should be preserved. Yet her advisers alone decided what would be turned over and should not, without any outside control or clarity on the process they used.

Earnest said "if in fact Secretary Clinton's team did what they say they did, and that is reviewed her email, collected all of her personal email that was related to her official government work and turned that over to the State Department so that they could properly preserve and maintain it, that would be consistent with the Federal Records Act. And that's the president's expectation."

Earnest also pointed out that the government runs a separate email system to exchange classified information, so classified information should never have been sent on an outside server.

Jerome Reisman, a New York-based attorney experienced in government ethics, said a private server gives the operator more control over their communications and makes it more difficult to subpoena electronic records as part of investigations. But he said the private server also has a greater chance of being exposed to hackers.

"This is not an issue necessarily of was it legal or was it illegal. It was wrong," Reisman said. "It is very important. It reflects on her character. It reflects on her role. It reflects on the model she serves to the rest of public employees."

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