It doesn't matter whether you left your documents in your house, or your neighbors if "they police find those documents otherwise lawfully." So I'm not sure wha

It doesn't matter whether you left your documents in your house, or your neighbors if "they police find those documents otherwise lawfully." So I'm not sure what your point is. I do have a reasonable claim of privacy if I leave a box of papers at my friends house. I can't claim that privacy if my friend gives the box to the police. But that doesn't give the police the right to barge into my friends house and take my property (without reasonable suspicion) Lets suppose the cops don't have reasonable suspicion to search my house for that box... If I give the box to a friend, and they don't have reasonable suspicion to search his house, they still don't have it, because I gave him the box. The only thing I don't have control of, is what my friend does with my box. In the Google case, I have a claim to privacy. I expect my mail to be private. It is my expectation, and the police should require the same warrants to get my data from Google than they would have to get it from my house.