Ladar Levison's article in The Guardian on why he had to shut down Lavabit:

My company, Lavabit, provided email services to 410,000 people – including Edward Snowden, according to news reports – and thrived by offering features specifically designed to protect the privacy and security of its customers. I had no choice but to consent to the installation of their device, which would hand the US government access to all of the messages – to and from all of my customers – as they travelled between their email accounts other providers on the Internet. [..]

Bothered by what the agents were saying, I informed them that I would first need to read the order they had just delivered – and then consult with an attorney. The feds seemed surprised by my hesitation.

The entire process was eye opening. He closes with a warning:

If my experience serves any purpose, it is to illustrate what most already know: courts must not be allowed to consider matters of great importance under the shroud of secrecy, lest we find ourselves summarily deprived of meaningful due process.