-- Mount black bag attacks on your premises. -- Snoop the networks of internet service providers.
On the other hand, most or all of the following are true of my keys-to-the-kingdom email account (the one from which most other passwords can be reset):
-- It is very unlikely to be hacked by any information guesses of my password, social engineering of my "secret question" information, shenanigans with my mobile phone, etc.
-- It is with a provider who seems less likely to get hacked than even Yahoo.
-- It has security that would be hard to brute force.
-- It has a unique password that I don't use on other, more vulnerable accounts.
Even so, I assume that all my communications are available to the US government, at least by after-the-fact subpoena if not actually real time.