Hmm, I'll have to do more research, but I thought they used some American hosting. Perhaps I'm mistaken! I'll make a note in the comment, ty!
edit: I take that back, I'm not wrong, yay \o/.
https://blog.fastmail.com/2013/10/07/fastmails-servers-are-i...
They are in the US, it's just that the company itself isn't. So depending on your level of distrust of the US, that may or may not be an issue for you.