That is defense 101. If you don't have it, they can't ask for it. Most of us keep e-mail for years or indefinitely. That means that the e-mail can be subpoenaed and used against you. If you delete it on a regular basis they can ask for it but no one has it. While the FED is required to keep records most other entities are not. Additionally even though the fed is required to keep the records it should be clear that they're staggeringly incompetent or willfully disregarding the requirement. A hard drive failure at the end user level should have no impact on the e-mail records which should be kept on a server somewhere.
Que the saber rattling and talking points to distract from some other dumb government idea/action.