Regarding PB on National Archives and Hunter emails, NARA implemented what is known as “Capstone” under their General Records Schedule (GRS) for handling emails government-wide. Emails from normal workers are only kept 7 years while senior officials are permanent. Many agencies put in methods to automatically capture emails under this so I bet dollars-to-doughnuts that those documents are currently living elsewhere and could be FOIAd, increasing the chance of success.