The Australian technology firm Fastmail is claiming to be beyond the reach of US law, including the National Security Letters used by the NSA. It states that it "does not co-operate with blanket surveillance" and does not give information on its users to anyone outside Australia.

Responding to growing public debate over online surveillance by the US National Security Agency, a blogpost from Fastmail to its users emphasised the fact that it is incorporated in Melbourne, and so only has to respond to demands made under Australian law, though it conceded that some of Fastmail's servers are in the US.

Robert Norris, Fastmail technical lead, said: “Australia does not have any equivalent to the US National Security Letter, so we cannot be forced to do something without being allowed to disclose it.

“We are required to disclose information about specific individual accounts to properly authorised Australian law enforcement with the appropriate supporting documentation, which means a warrant signed by an Australian judge,” Norris says.

“We do not co-operate with any kind of blanket surveillance, monitoring or ‘fishing expeditions’, and we do not give out user information to anyone outside Australia. We do not have a legal presence in the US, no company incorporated in the US, no staff in the US, and no one in the US with login access to any servers located in the US."

Fastmail became an independent company in September following a staff buyout from browser developer Opera. Two secure email services, Silent Circle and Lavabit, have been forced to close recently after pressure from security agencies, while others, including a new service in Germany, are making a selling point of protecting user data from the NSA.

Norris specifically addressed the issue of Fastmail's server location, and said even if its servers were seized, consumer data is protected by encryption.

“Even if a US court were to serve us with a court order, subpoena or other instruction to hand over user data, Australian communications and privacy law explicitly forbids us from doing so. We can make it extremely difficult for these things to occur by using strong encryption and careful systems monitoring,"

Last week, the creator of PGP encryption Phil Zimmermann pointed out that no security model can overcome the intrinsic flaws of email. PGP, short for “pretty good privacy”, can protect the contents of messages, but message headers (which reveal the sender, recipient and time of the email) can never be hidden.

Mike Janke, with Zimmermann the co-founder of Silent Circle, a secure communications company, described email as “fundamentally broken”.

• Why does a major security firm think email is fundamentally broken?

• This article was amended on 9 October 2013 to clarify that Fastmail did not claim to be "NSA proof".