use by law enforcement in putting together a case. For the purposes of reading the email the vast bulk of all US emails are already being examined by the NSA computer systems as the electronic communications interception system known as Echelon can lawfully collect and examine all communications that cross the USA borders, and that includes any that go via a satellite link as they're in International space being above the US boundary, and any that cross over into Canada or Mexico to use their pipes for delivery. The same applies to all Internet traffic too.