Microsoft today made its case to the U.S. Second Circuit Court of Appeals in a legal dispute between the company and the U.S. government, in which Microsoft is challenging a U.S. search warrant for customer email stored on a server in Ireland.

The company’s brief takes the unusual approach of beginning with a hypothetical example.

Imagine this scenario. Officers of the local Stadtpolizei investigating a suspected leak to the press descend on Deutsche Bank headquarters in Frankfurt, Germany. They serve a warrant to seize a bundle of private letters that a New York Times reporter is storing in a safe deposit box at a Deutsche Bank USA branch in Manhattan. The bank complies by ordering the New York branch manager to open the reporter’s box with a master key, rummage through it, and fax the private letters to the Stadtpolizei.

Of course, as the filing goes on to note, the U.S. government would be up in arms if that happened.

“If the Government prevails, how can it complain if foreign agents require tech companies to download emails stored in the U.S.? This is a question the Department of Justice hasn’t yet addressed, much less answered,” writes Brad Smith, Microsoft’s general counsel, in a post today. “Yet the Golden Rule applies to international relations as well as to other human interaction.”

Microsoft lost the initial ruling in a lower court, leading to the appeal.

In a previous filing, the U.S. government called Microsoft’s arguments “entirely incompatible with the express text of the statute, which orders service providers to disclose records upon receipt of a warrant or other appropriate legal instrument.” It added, “Nothing in the text or structure of the statute carves out an exception for records stored abroad, and none exists in precedent construing the scope of compulsory process.”

Stay tuned, we’ll continue to follow this case as it proceeds through the courts.