The Justice Department asked a federal magistrate if it could check up on unsuspecting (and not necessarily suspect) email users, but instead of looking at contents, they wanted email header info instead. The magistrate balked, so Justice brought a friendly judge in to seal the deal.
Why would they do such a thing? Let me guess.
I just sent myself an encrypted email message, using everyday old (but extremely strong) PGP software, and turned off the decryption engine a moment later. Whoops, it just arrived back, message garbled for all eternity. But wait…lookee there! Plenty of header information for a paranoid prosecutor to flash in front of a court (smoke and mirrors close at hand, of course), in order to get a deeper surveillance warrant.
Nice. And useless.