At a rally in Grand Rapids, Michigan, he said he hoped the Democratic candidate's 33,000 deleted messages could now be recovered.
The FBI is investigating new emails that may be linked to its probe into Mrs Clinton's private email server.
Mrs Clinton later told a rally she had nothing to hide.
It emerged in March 2015 that Mrs Clinton had been breaking federal rules by operating a private email server while she was secretary of state from 2009-13.
Her lawyers combed through the server and provided the State Department with 30,000 work-related emails.