At the end of the day, the lynchpin of the 4th amendment is an
objectively reasonable expectation of privacy. Not merely a subjective desire that the government not see certain information.
With that in mind, I just don't see how you can say you have an objectively reasonable expectation of privacy over e-mails in the cloud, when a system operator can pull up all your personal information going back years at the touch of a button. When the e-mail service not only has incidental access to the data, but actively looks into that "private" data and uses that "private" data for commercial purposes. It's a distorted, results-oriented definition of "privacy."
That said, you're likely going to get precisely that results-oriented interpretation, because apparently the Supreme Court, like most users, doesn't fully understand the scope of how cloud providers access and use and commercialize your data.