My department, in DoD, sets encryption on as default. It's a pain in the ass, so most turn it off from default. Encryption is available to everybody with a common access card.
The private encryption key for e-mail is escrowed by DoD, so it can be retrieved to decrypt the emails if necessary.
Our disk drives are also encrypted with a similar private key.
DG Brown,
I want to expand upon Indispensable Destiny’s accurate description of DoD encryption of e-mails. It is done for an additional level of security against hackers and to protect personal privacy information. It is NOT put on by individuals but is a DoD wide system and anyone receiving an encrypted e-mail via the DoD e-mail system can decrypt the e-mails using their Common Access Card, which gives them access to their computer and e-mail. This is not a system that prevents unclassified e-mails to be exempt from FOIA requests. Dealing with classified e-mails is via the SIPRNET system which is entirely separate from the day to day e-mail that DoD and other federal government employees use. I was such an employee with the Department of the Army until I retired a few months ago. Whatever encryption system the DoJ/FBI folks are using, is completely different from what I-D and I are discussing...and may very well be illegal. Unfortunately I’m not familiar with it.