It wasn't so long ago in America that having a private email server was actually the main complaint about a presidential candidate. Everyone knows that they all do it one way or another.
Conservatives are vibe haters. They feel something is wrong and will figure out how to justify their feelings. The email server was just one of many excuses to dislike Hillary. But it was never the "main" one. It was just one that gained a lil traction.
Hillary also caught crap for Benghazi, her husband, her aides, her outfits, etc. It never ends with conservatives because how they feel is as important as reality. They'll find anything to justify their vibes.