White House probing private email use after revelations about Kushner and others At least six senior officials used private email to discuss official business.

 -- The White House is conducting a performance review of all staff members to ensure compliance with policies related to the use of private email accounts, two senior administration officials told ABC News.

The review, which is being led by the White House counsel's office, comes after revelations that at least six senior officials, including President Donald Trump's son-in-law and senior adviser Jared Kushner, have used private email to discuss official business.

The probe is focused on emails on the White House server sent to and from the private accounts of all staff, sources said.

White House press secretary Sarah Sanders responded to reports Monday of Kushner's use of private email, saying that staff "are further instructed that if they receive work-related communication on personal accounts, they should be forwarded to official email accounts.”

Spokespersons for Kushner and his wife, adviser to the president Ivanka Trump, said that their emails have been preserved.

All West Wing staff are required to comply with the Federal Records Act, ensuring any personal emails related to government business are preserved as official records. Officials said the policy was thoroughly articulated to staff during the transition and enforced from day one.

The internal White House review comes after the leaders of the House Oversight Committee opened an investigation earlier this week into the use of private email and encrypted communications software at the White House.

On Monday, House Oversight Committee Chairman Trey Gowdy, R-SC, and Rep. Elijah Cummings, D-Maryland, sent letters to the White House and 24 federal agencies requesting an update on efforts to comply with federal record-keeping policies.

The panel also asked the White House to identify any staffers using personal email addresses or encrypted messaging applications for official business.

"If you're going to engage in public work, you need to create a record related to that work, you need access to it, the public needs access to it, Congress needs access to it," Gowdy said in an interview with ABC's Mary Bruce.

Gowdy, who led the House Benghazi Committee that discovered Hillary Clinton's use of a private server as secretary of state as part of its probe into the 2012 Benghazi attack in Libya, said he has the "same questions" for the White House and Kushner as he did for Clinton.

"I'm doing the exact same thing I did with her. Which is show me the facts," he said. "I'm not just singling out the ones I know about. I've written everyone that's in the administration that I could think to write. So, I'd like to same standard to apply whether it's Republican or Democrat. I know that puts me in a small minority in this town. But the same questions that I would ask her, I'm gonna ask of folks in this administration."

Cummings also wrote separately to Kushner seeking additional information about his private email use.

"We want to know whether he - first of all, how long he was using these, this personal domain. And what he did to protect any classified information. We also want to know who he was communicating with," Cummings told ABC News.

Democrats have criticized the White House for hypocrisy following news of private email use at the White House in light of President Trump's attacks on Clinton during the 2016 presidential race.

But there are differences: Clinton set up a private server for all of her work email use at the State Department, which prompted questions about the mishandling of classified information. The FBI eventually cleared Clinton just before the 2016 election after a yearlong investigation, finding that she did not knowingly send or receive classified information.

White House employees are not prohibited from using personal email, but must forward all work-related messages to official accounts for record-keeping purposes. Government officials are required by the Federal Records Act to create systems to record and preserve emails, notes and other documents related to official government work.

Abbe Lowell, an attorney for Kushner, told ABC News in a statement that Kushner sent or received less than 100 emails from White House colleagues on his personal account, and that the messages were "usually forwarded news articles or political commentary."

ABC's Mary Bruce, John Parkinson and Benjamin Siegel contributed to this report.