RE: Reasonable expectation of privacy.
The issue covered by the judgment is not one of the security of the transmission of e-mail. It's all about the requirement of law enforcement officials to get the court's approval, in the form of a warrant, to search for suspected evidence.
The law enforcement agency was contending that if the data is still on the server of the provider they don't need a warrant. That they can bypass the court's oversight by going to the e-mail provider and demanding (or requesting) they hand over the messages.
In saying that, they are basically asserting that once an e-mail message is in the hands of your provider, you have put it into the 'open field' (a.k.a. public view) and it is therefore not subject to warrant requirements. This would be comparable to leaving your bank-robbery plans on the table of a restaurant: the police don't need a warrant if they convince the restaurant owner to give it to them.
Several rulings have been made on very similar matters...
The courts have always finally ruled that the authorities can't skirt the requirement of a warrant by getting the data from a storage facility. The originator of data has a reasonable expectation of privacy in that a storage facility, being that they are not the owner or recipient, has no inherent right to use the data. Therefore sending it through or storing it with them is not putting it into the open field, which means they have no right to hand it over to the authorities of their own accord... and that means that a warrant is required.