Most email providers who provide 'privacy' like this will hand your details to a government authority if the appropriate court documents are issued - with the case of Hushmail, they were forced (or asked) to exploit a loophole in their encryption system to capture a steroid dealer, I believe. I would NOT trust any email provider who is offering said service if you are going to use it for dubious things that the authorities might be interested in. With that said, if you are adamant on it, use a strong form of masking your IP (like with Tor) and an email provider of your choice.
If you don't already know about Tor, I suggest you go take a read here and elsewhere online: https://www.torproject.org/