Her personal system administrator, of which there are many had access, unless you think they setup a multi-level security email server with proper encryption, which based on the FBI report they did not. The FBI proved that those people had access to the email. They could not prove that others did because Clinton had the evidence destroyed and the remaining server had been cleared of most data. So it is an unknown if crackers and other government actually provide they have the info instead of just claim they do.
No need for others to show that she transmitted/broadcasted classified information because the FBI report said she did. This came down to a decision that because the evidence was destroyed and she was able to prove she was incompetent that there was not enough to prove in a court that she broke the law.
As for Bush go back and read the many, many news reports that came up out that that. Bush, and others in his office, were doing it somewhat correctly. They were using a separate system for personal and non-federal business. The problem from that came when people would be on the non-federal business account and would send off email to a federal address. To fix that different laws were put into place.
So what laws did Bush violate? Also why is Clinton so incompetent (according to the FBI) and stupid that she did not remember all the news articles about the Bush administration and that new laws that were put into place to make sure that happened under Bush would not happen again?