To respond to both of you above. Setting up two of these at once would have increased both the up-front cost (hardware for something like this is well north of a million USD) and the complexity and associated risks. Yes, it's partly a "people want it for their own reasons and we should offer it if it's viable" and partly a "it's good to have service in multiple jurisdictions and experience with them in advance of any further balkanization of the internet".

Re-launching might be costly, but dropping millions more on a second location and splitting our systems more would hav been much riskier (note: many of our customers with 'fastmail.com' addresses have chosen the EU region, we can't segment MX records at a tighter boundary than domain level).

So we do what we can - when you login with username and password, the password is only sent to your region's server (based on a lookup from the username which MUST be global, so it works regardless of which of our servers you hit). If you send a username which doesn't exist, we distribute you to a random region in the same percentage, so you can't use it as an existence oracle.