Williams & Connolly, the law firm of Clinton’s personal lawyer David Kendall, gives the FBI a thumb drive which has a .pst file containing 30,524 emails. On December 5, 2014, Clinton’s lawyers gave the State Department 30,490 emails, sorted to be all of Clinton’s work-related emails. It isn’t clear why there is a 34 email difference.
On July 31, 2016, the Justice Department asked Kendall to turn over his thumb drive.
Clinton lawyer Heather Samuelson put the .pst file on a thumb drive and gave it to Kendall around the above-mentioned December 5, 2014 date. (Federal Bureau of Investigation, 9/2/2016)