From The New York Times report, here:
The State Department said on Thursday that 15 emails sent or received by Hillary Rodham Clinton were missing from records that she has turned over, raising new questions about whether she deleted work-related emails from the private account she used exclusively while in office. ... State Department officials then crosschecked the emails from Mr. Blumenthal with the ones Mrs. Clinton had handed over and discovered that she had not provided nine of them and portions of six others. Nick Merrill, a spokesman for Mrs. Clinton, who is running for president, said that she had given the State Department “over 55,000 pages of materials,” including “all emails in her possession from Mr. Blumenthal.”