Feel free to hit the "delete" button on your incriminating Microsoft Exchange e-mails. Even if you do so with the intent of keeping those e-mails from the Feds, the Ninth Circuit says that doesn't count as obstruction of justice. Because you haven't "concealed" them; you've simply moved them from one folder (e.g., your inbox) to another (e.g., the "deleted items" folder). That's no different from, say, moving an incriminating document from the top of you desk to a desk drawer.
You may not be entirely off the hook, however. The Ninth Circuit doesn't decide whether hitting the delete button (or moving the e-mails to the "deleted items" folder, which is the same thing) counts as attempted obstruction of justice. The Ninth Circuit similarly doesn't decide whether "double deleting" e-mails -- i.e., moving them to the "deleted items" folder and then "emptying" that folder -- counts as obstruction of justice. So you've still got look out for that.
But if all you do is to move files into the deleted items folder, that ain't going to subject you to non-attempt liability. Mind you: It won't stop those e-mails from being discovered by the government either, since it'll perhaps not shock you to discover that they actually check that folder (and more!) once they seize your computer.
But if all you do is hit the delete button, even with an evil intent, your malicious incompetence may well not count as a substantive federal offense.
Good to know.