I suspect that China and Russia were only two of many countries and other actors who acquired the stuff off he sieve she called a server.
Start by looking at the contributors to the Clinton Foundation. For enough money, she would give a password so they could "hack" into her email server.
I suspect the whole server thing was set up as a way to get intelligence to countries who paid her and be able to make herself look like a victim of hacking if she was caught.
The intelligence services of Botswana and the Maldives were reading Clinton’s emails before she did.