Re: Get them from the account holder
Well, there's this funny thing in the US called the constitution and one of the things it specifies is that people cannot be forced to incriminate themselves. This has already been tested and found to apply to passwords and PIN codes.
I don't know if it's also been tested wrt usernames, but it seems likely that those would fall under the fifth amendment as well. So the US government cannot force a suspect to give up login details in order to retrieve e-mails.
Now, IANAL, but obvious law is obvious. If the user and company both reside in the same jurisdiction, then that jurisdiction's laws (and thus court orders) should apply, regardless of where the data is stored. If the user and company reside in different companies, the laws in the user's jurisdiction apply to him, but court orders will need to be obtained in the country the company operates in.
Physical location of the data is as stated irrelevant in this manner, provided that this is internationally agreed and enforced. Of course it'll never happen because it means the US won't be allowed to spy on everybody any more.