Let me add a little more to this thread and keep it civil and avoid politics.
1) I believe NSA has the ability to unencrypt and read any email from anywhere. I don't know this for a fact but it is highly likely. Therefore no email provider is safe from this. This is not a new revelation. This is not a Bush mandate. This is what they do.
2) Although possible I don't think they would share this with DEA. The reasons are that first of all this is extremely sensitive capability. There is probably only a small group in NSA that has this knowledge with the proper security clearance and "need to know". They would be extremely hesitant to share this with anyone for fear it would fall into the wrong hands and possibly compromise our own military and govt. which uses some of it.
3) Typically from what I have seen DEA gets supoenas for peoples mailboxes if they have reasonable cause such as making buys from them. US companies would be bound to comply with this court order but overseas would not unless there is some type of agreement with that govt. We have seen that hushmail, although overseas has complied so I would completely avoid them.
4) My advice would be to use an overseas email service that has shown it will not comply with supoenas/requests for email info. I am not sure if there are any that fit this mold but would like to know myself. Perhaps some others can help answer that.
5) I do not know any of this above to be a "fact". It is my educated guess based on a small amount of info over the years. If others have evidence to show otherwise I welcome it. My advice when it comes to gear is not to worry about NSA, they really don't care about you, but do indeed worry about DEA, especially if you are a source. Analyze every bust to see how they did it, how they got their info, and learn to avoid those pitfalls or mistakes which have gotten others busted. Stay safe.