The case is "In The Matter of a Warrant to Search a Certain Email Account Controlled by Microsoft Corporation" [1,2]

In this case, it's about an e-mail account provided by Microsoft (an American company) but physically hosted in Ireland.

[1] http://www.reuters.com/article/2014/04/25/us-usa-tech-warran... [2] http://www.computing.co.uk/ctg/news/2341902/us-court-cloud-c...