Ignorance of the law is never a defense.
In order to convict someone of a non-strict-liability crime, that person must have something called a mens rea, which is a fancy legal term that basically means some level of intent, and an actus reus, which means a guilty act. For most crimes you need both mens rea and actus reus to convict.
Every crime has a different degree of mens rea required to convict. For example, a murder charge must allege that the killing was done with malice. I am assuming that the mens rea for the espionage act crime requires a "knowingly" mens rea, which means that Hillary must have intended to commit espionage by exposing her emails to foreign hackers. That clearly isn't the case, so no indictment. In fact, it seems that merely exposing emails to the possibility of foreign hacking is not in itself illegal. That means there is no mens rea OR actus reus for Hilldawg.
Knowledge of the law is simply irrelevant. If you steal something and say in your defense that you did not know that stealing was illegal, the prosecutor will laugh at you. If you instead say that you were not aware that the item was not a free sample, for example, you would lack the requisite mens rea for theft.