Hillary used a private email server - which she had complete control - to conduct official business during her tenure as Secretary of State. Whether that's illegal is not nearly important as the reason for this wavering from official policy she strictly enforced with others in the Department of State.
I think it's safe to assume incriminating emails are now gone. While Hillary might not have this expertise, she could hire someone to remove the information. That's where there are other ways to find these email.
The computers of all in the White House, important members of the administration, and Congressional members could be seized with a search warrant, but it would take a willingness by the Department of Justice to pursue the matter. I don't see this happening, but the lure of money could yield some interesting information.
How about a cash award for emails from people that can be persuaded to trade cash for immunity? I think this would work. After all, when ethics, morals, and honesty are far removed from daily thoughts, the lure of money is a powerful tool.
This is a suggestion to members of Congress investigating; and for those with political agendas to remove the criminal elements in political power. Grow a set and do something useful.