“To address misinformation being peddled about Ms. Trump’s personal email, she did not create a private server in her house or office, there was never classified information transmitted, the account was never transferred or housed at Trump Organization, no emails were ever deleted and the emails have been retained in the official account in conformity with records preservation laws and rules,” the spokesman, Peter Mirijanian, said in a statement. “When concerns were raised in the press 14 months ago, Ms. Trump reviewed and verified her email use with White House counsel and explained the issue to congressional leaders.”

Ms. Trump had told people in the White House that she was unaware of the rules when she was using her personal account.

But her repeated use of her personal email on a private address, ijkfamily.com, which was set up by Mr. Kushner and Ms. Trump during the transition, was a cause for concern within the White House counsel’s office, according to two people familiar with what took place.

The liberal watchdog group American Oversight said on its website that its freedom of information requests had led to the discovery of the volume of Ms. Trump’s email use. The emails obtained by American Oversight showed exchanges with the commerce secretary, Wilbur Ross, and other top personnel at agencies.

“The president’s family is not above the law, and there are serious questions that Congress should immediately investigate,” Austin Evers, the group’s executive director, said in a statement on the website.

After Ms. Trump’s personal email use was discovered, Mr. Lowell helped sort out what emails qualified as official records that needed to be kept for posterity, The Post reported.

That was similar to the approach Mrs. Clinton used when she was sorting through tens of thousands of emails.