Yes, really. Congress saw fit to make gross negligence the standard of guilt for the crime defined in U.S. Code Title 18, section 793(f), which is a small portion of the Espionage Act of 1917. Here is the link to the federal code, and I will also reproduce the text:
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(f) Whoever, being entrusted with or having lawful possession or control of any document, writing, code book, signal book, sketch, photograph, photographic negative, blueprint, plan, map, model, instrument, appliance, note, or information, relating to the national defense, (1)
through gross negligence permits the same to be removed from its proper place of custody or
delivered to anyone in violation of his trust, or to be lost, stolen, abstracted, or destroyed, or (2) having knowledge that the same has been illegally removed from its proper place of custody or delivered to anyone in violation of its trust, or lost, or stolen, abstracted, or destroyed, and fails to make prompt report of such loss, theft, abstraction, or destruction to his superior officer-
Shall be fined under this title or imprisoned not more than ten years, or both.
The text could not make more clear that no intent is required for this felony. It may be committed in two ways: 1) through gross negligence; or 2) through failure to report the mishandling of any of the documents described. The first of these is the one which applies to Mrs. Clinton's actions.