Yes! They know. At the least, they imagine what might be in the emails and can only come to one conclusion: she is toast.
Now, what could possibly be the basis for surmising such a scenario?
I compare this whole email/server thing to a guy that has been surfing pr0n and communicating with his girlfriends on his computer, but trying to use simple “free” tools to delete his activity.
And one day his wife has his computer removed and gives to a forensic company to find out what’s on it. He’s saying “Hey, baby, there’s nothing there.” But then the forensics guys find something relatively innocuous, but something he thought he deleted.
So now he’s sweating.
As is Hillary, apparently.