"Getting my data back under control
In the past months we’ve had a lot of scary revelations about privacy violations, the biggest being of course the NSA spying scandal. It became urgent to regain control of my data."
If someone else is hosting your e-mail, then you do not have your data "under your control". A government can still compel Fastmail to turn over e-mails via legal process (as they should be able to, to be honest). Additionally, there's no evidence that FastMail (or any other e-mail provider) is better protected from NSA infiltration [1].
It seems like the author has plenty of other reasons to switch, but this one lends nothing but a false sense of security [2].
[1] Possible exceptions being Lavabit-esque systems that do client-side encryption or Google itself, which has begun encrypting their internal as well as external traffic.
[2] Not that I really recommend running your own e-mail server either. Setting one up (and maintaining it) is so error-prone that you're probably even less safe than before.