Hillary knew a lot more about servers than she pretended:

Yeah, she basically at the end of the 2008 campaign instructed one of her close aides to download the emails of some of her top campaign advisors to figure out who’d been talking to the press, who’d been doing the backstabbing, or presumably if anybody had been talking bad about her, and because she felt that this loyalty was a huge problem for her in 2008. So what she did was figured out how to get all these emails. Now you know, a few years later, she’s making the argument that she didn’t understand what she was doing in setting up a private server outside the State Department system. But it’s very hard to, it’s very hard to reconcile the idea that she understood well enough that she could download her own aides’ emails, but didn’t understand that by putting a server outside the State Department, she was basically preventing people from getting her information during a campaign season, unless of course as happened, there was a court order to retrieve those emails.

We know why she set up the server, and it wasn’t “for convenience.” Other than it being inconvenient for her if people found out what she was really doing. She probably did lie to the FBI, but Comey was either in the tank for her, or a political coward.