The spying on emails is in violation of the Us constitution. And under executive order 13526, section 1.7 – you can not classify information to just cover up a crime, which this is, and that was signed by President Obama. Also President Bush signed it earlier as an executive order, a very similar one. It appears that the US government is seeking to prevent the matter from coming before the Supreme Court less that body finds their actions to be unconstitutional.
Personally I'll put more reliance on email encryption than on US constitutional lawyers.