At a glance this seemed like an obvious move, but the deeper you look everything stops making sense.
The emails between company officers suggest that they themselves used their own service to upload copyrighted content and share it with others, knowingly breaking the law. Case closed!
But what gives US law enforcement the right to obtain those private emails between officers of a foreign company? Reasonable suspicion of infringement? What suspicion? Suspicion of failure to comply with DMCA takedown notices?
What is the basis for that suspicion? Their failure to delete ALL links to any file for which a single link is reported. But as many others have pointed out, each of those links represents a specific user who has uploaded the same file. Without a public searchable index, each of those keys is effectively a distinct privately uploaded file.
So we come down to whether a copyright holder has the authority to say "anyone anywhere who has uploaded a copy of this file, does not have the right to share it".
What next? If a service like Dropbox borrows a hint from git and stores not just single file hashes, but distinct unique data chunks, and a takedown request calls for the deletion of say, a feature film, will they claim Dropbox knowingly infringed for failing to remove a 10 second chunk of that film that some student put in their dissertation?