Originally posted on 10/09/2016:
You, I and many others who have operated under clearances are free to 'delete' emails because we access them on secured networks, with admins implementing retention policies to comply with applicable laws and ensure our 'deleted' emails are retained as needed. Setting up your private server puts the burden of retention on you instead, and when you don't retain it, you're violating those laws.
Considering the all-but-certainty that her team reacted to the subpoena by ensuring records were erased (instead of attempting to recover them), it's a fairly relevant condemnation of her dishonesty.