That's where the "minimization" documents from last week come in. They actually collect everything, but then there is some kind of filter at the collection poin

That's where the "minimization" documents from last week come in. They actually collect everything, but then there is some kind of filter at the collection point that is supposed to remove any communication that they are certain is american-to-american. But that filter also has exceptions for things like encrypted messages or pretty much anything else they are interested in. They make the filter as loose as they can while still being able to maintain some deniability that they don't collect domestic communication.