DOS is Department of State?
I knew about the Coast Guard, but I didn't know you worked at the State Department too.
If you want to say that she went the private server route to keep her communications private and not subject to FOI requests, I would agree with that. Hillary is very careful to not hand out ammo to her political enemies, 30 years of Republican investigations have taught her that.
But I do dispute that other SoS haven't done that, both Colin Powell and Condi Rice did it, or their staff did it on their behalf. The rules were updated when Clinton left office to ensure that future SoS's did use government systems, I think they had some leeway before then.