From what I can tell it is based in the US and they clearly state that they will reveal information or co-operate with authorities where they are legally obliged to do so. It also says nothing on how the emails are stored. I'd only trust an email service which encrypts its content in such a way the operators themselves cannot read the content even if they wanted to and then have a court case or public record to prove they were unable to help authorities, ie, failed prosecution of users for being unable to read e-mail content.