I would think that a system set up for personal use in a basement does not have the same security that a State Department email server has. I'm sure that our government could still get into the system. And if our government can, then foreign governments may be able to hack into the system. An email server by definition is connected to the Internet and is vulnerable to hacks along the email route. Her email was discovered when the hacker hacked Sidney Blumenthal’s email, so it wasn't so secure after all. At least if she had been sending her email through the State Department, there would have been more checks along the way.
She set up a private server so she could completely delete what she didn’t want anyone to see, she couldn’t do that with govt email.
With her private server, from what I understand and the way Rush described it, she wouldn’t even need to actually send an email to exchange information with someone.
Apparently she could put an email in draft and not send it then someone else could open that account read the draft and delete it and there would be no record.
That person in turn could respond by drafting a message but not send it, Hillary could read it then delete it.
This is what Petraus was doing and he got caught because apparently he was using govt email.