Honestly, I don't see how this doesn't splatter on 0. He was nominally her boss, and yet he allowed her to break the law? When he is sworn to execute the laws (not that that's ever stopped him)? He MUST have sent her at least one email in 4 years, therefore he can't claim ignorance.
Personally, I like Allen West's take on it: Hillary at the least concealed her emails by having her own server and not submitting them to DOS. This is a felony that carries not only 3 years in prison (I wouldn't dare hope that she'd get that), but permanent disqualification from holding office ("and shall forfeit his office and be disqualified from holding any office under the United States").