I don't think Fastmail is very clear on their privacy policy (see also my other answer below).

Here is an extract from Fastmail TOS:

Fastmail can disclose your info/data if it thinks it's in the interest of the company: "The Service Provider will not monitor, edit, or disclose any personal information about you [...] unless required or allowed by law, or where the Service Provider has a good faith belief that such action is necessary to: [...] (2) protect and defend the rights or property of the Service Provider; [...] (4) act to protect the interests of its members or others [...]