Lavabit abruptly shuts down
For the unfamiliar: Lavabit was a webmail service, that (claimed to) encrypt emails in such a way that they literally did not have access to the content stored on their own servers. The linked email would lend some credence to those claims. It was originally designed in contrast to gmail scanning your email for targeted advertising, but my imperfect memory says that their system should also have been resilient to "we have a warrant, hand over the data."