Hillary Clinton emails scandal: Will the FBI cost Hillary the election?

Even if you've - with good reason - tapped out of reading about the ongoing US election, it's impossible to miss headlines about Hillary Clinton's emails.

The ongoing controversy, referenced as often as possible by Clinton's critics, is complicated, as it touches on different incidents and pre-existing scandals.

Here's what you need to know about Clinton's private email server, missing emails, and the controversy swirling around "emailgate".

Hillary Clinton email hack: what you need to know

What happened?

Clinton ran her own private server to send and receive emails, setting it up just before she became Secretary of State in 2009 and using it for both work and personal messages, and setting up members of staff on the same system.

She didn't use an official State Department email account, but if she had, it would have been on US government servers.

That system was revealed following the Benghazi incident - don't ask us to get into that, read up on it here - which led to journalists and government officials alike demanding her work correspondence related to the attack. However, the State Department in 2014 said it only had eight messages from Clinton, which sounded a little on the low side.

A year on, The New York Times ran a storyaddressing that question, revealing Clinton used a private server.

Why would she do that?

There's two answers to this: what Clinton has said and what critics have inferred.

Clinton has repeatedly said the private server was set up for reasons of convenience, as it allowed her to carry a single smartphone with her, as government BlackBerry smartphones couldn't at the time manage dual email accounts.

However, an FBI investigation revealed she still carried "numerous personal devices" and has a large staff that could have managed any extra smartphones for her.

Of course, running a private email server had other benefits beyond make more room in her purse, notably allowing Clinton and her staff control over what messages they handed over to the government, either for its own investigations or for freedom of information requests.

Either way, it's been suggested she got the idea from a former Secretary of State, Colin Powell, who also used a personal account during his time with the State Department.

What's happened to the emails since?

After months of pressure - which didn't exactly inspire confidence in her willingness to disclose official messages - Clinton released 30,000 emails via the State Department. She said those were the only work-related messages, but the FBI found a few more thousand as part of its investigation after she handed over her server - though it said they had been missed because they'd been deleted years prior.

Did Hillary Clinton break the law?

An internal investigation said Clinton's private email server broke government rules, but the FBI said no prosecutor who was "reasonable" would bring charges.

Over the time Clinton served as Secretary of State, the rules around emails changed slightly. At the start of her term in office, the rule was that any government staff using a personal account must hand over official messages to the government to archive. Part way through her term, it shifted to only allow private email accounts if official messages were "preserved" in formal record keeping.

Clinton has argued her server keeps with both rules, mostly as she was sending the bulk of the emails to others in government who would be officially archived. Even if her system didn't meet those requirements, the rules are internal policy, not criminal law.

Why does any of this matter?

As noted previously, the use of a private email server depends on Clinton to share her emails with the government and in turn the press - and she infamously prefers to keep her cards close to her chest and has been accused of not being very keen on transparency.

However, some have pointed out that phone calls aren't subject to the same freedom of information act requirements, so she could have avoided transparency simply by picking up the phone to make a voice call.

That aside, Clinton's setup raises the question of whether her email was ever hacked. Clinton says the account was secure, and there's no evidence it was hacked, but the FBI has said she used it to send classified information, leading Clinton to be called "extremely careless". Plus, hackers simply could have covered their tracks, making it difficult to know if there was a breach or not.

That said, the State Department's own email system was itself the victim of a massive hack in 2014, so her messages may not have been safe even if she did stay inside government systems.

All of that makes for good ammunition for her critics, in particular Republican nominee Donald Trump, who has repeatedly referred to his rival as "crooked" and suggested he would prosecute her if he wins the election.But then again, he's made many promises that aren't likely to come true should he become the next American president.

Plus, it's worth noting that her fellow private email fan, Colin Powell, is a Republican, as are others accused of similar problems, from Jeb Bush to Mitt Romney - making private emails a cross-party problem.

Why did the FBI re-open the email investigation?

The FBI re-opened the investigation into Clinton's e-mails 10 days before the US election.

Director James Comey told Congress he had re-opened it due to the discovery of 650,000 emails found on a laptop shared by Clinton aide Huma Abedin and her estranged husband, Anthony Weiner, during an investigation into an alleged sexting case involving the latter.

Clinton's campaign questioned the timing and reasons behind the FBI's decision, while Donald Trump suggested the emails could be ones that were deleted from the server before the FBI could get hold of them.

Democratic vice-presidential candidate Tim Kaine stated he found the timing of the FBI's decision "unusual", at a rally in Michigan.

A group of around 100 former federal prosecutors and officials from the Department of Justice, including Attorney General Eric Holder, wrote a joint letter in which they expressed concern over the FBI director's decision to tell Congress about the re-opening of the investigation.