To be fair, they also explicitly point out in their docs that encryption on their end is pointless (since they have the keys) and that you should encrypt your e-mails on the client side with something like PGP (where you control the keys).

E-Mail sucks, that's all. Fastmail is transparent about it and does a good job.

(PS: I still think that they encrypt their storage servers, but again, this will only protect against someone physically taking away their servers, not against a warrant or an intruder.)