The extremely secure email service used by Edward Snowden has closed – with the owner implying he is under pressure to release user data. So where should you turn now for encrypted email?

What was Lavabit? It was an extremely secure email service, set up by a group of programmers in Texas in 2004.

Are normal emails not secure? Not really. On Gmail, for instance, you may notice an ad at the top of the page that has been personalised by scanning the contents of your inbox. Google points out that "no humans read your email in order to show you ads", but that's discounting the NSA, which can nose around almost anywhere it wants, as you may have heard.

What made Lavabit different? A key selling point was something called "asymmetic encryption", which came with the "enhanced" and the "premium" account, which cost $8 and $16 a year respectively.

And what is asymmetric encryption? It's a complicated way of scrambling email messages to prevent the wrong people reading them. You have your own password that encrypts and decrypts messages, and this is linked to a different one that is used by the people who read and write them. The scrambling would happen before your messages were downloaded on to Lavabit's servers, meaning that they couldn't read your emails even if they wanted to, and nor could any government agency, unless they had your password.

Was it completely unbreakable? No. Nothing is. Codes could theoretically be intercepted en route between computers, or cracked inside yours, but the amount of work involved in that would deter most casual snooping.

Could Lavabit be forced to release what it has anyway? Perhaps. In June, the company complied with a warrant concerning a child pornography suspect in Maryland. The announcement from Lavabit's owner, Ladar Levison, explaining why he is shutting it down also implies that he is being put under pressure to release more.

Who used Lavabit? Edward Snowden, apparently, with the rather unsecretive email address edsnowden@lavabit.com. Plus about 350,000 other people who mostly prefer to remain anonymous.

What should I use now? That's difficult. There are a lot of email encryption services available, but Lavabit may not be the last specialist company to come under unwanted scrutiny. Another company, Silent Circle, has already shut down and deleted its email service because its co-founder Jon Callas claimed he could see "the writing on the wall". As Levison put it, in his message to Lavabit's users: "This experience has taught me one very important lesson: without congressional action or a strong judicial precedent, I would _strongly_ recommend against anyone trusting their private data to a company with physical ties to the United States."