Log analysis
"the identity of any non-Gmail users can only be found out if someone goes through all the non-Gmail users whose addresses are on file in its systems and then sifts through the responses"
That's a really difficult job. If only some big search engine company had some sort of toolset for processing large log volumes ... maybe they could call it Google Sawzall, like Google did when they created it over a decade ago?
I'm not too convinced of the case's merits, but the idea Google of all people can't process their own logfiles to find the names in question?!