Sending an e-mail is a bit like sending a postcard, in that it can be read by all and sundry on its way from the sender to the recipient. Not, though, if you subscribe to XenoMail from Indicii Salus, a service that lets you encrypt messages so that only the intended recipients can read them. It also lets you digitally sign messages, to prove who you are, and does all this using very secure public key technologies about which, fortunately, you need know nothing at all.

Still, a little background knowledge won't hurt. So for those who want to know, the following is what's involved, starting with the software. This comes in two parts, the first of which is a client for use with Microsoft Outlook (Lotus Notes is also supported), which can be downloaded from the Indicii Salus Web site. A simple setup routine integrates this into the mail software being used, adding extra icons on the toolbar to log on and off from XenoMail, set the type of encryption to apply and so on.

Then there's the Xenophon server which is where all the hard work is done, generating the public/private key pairs required to encrypt and, later, unscramble messages. However there's no real need to worry about this bit, as Indicii Salus hosts the Xenophon servers. All you do is pay an annual subscription to use them.

The system itself works as follows. Register as a XenoMail user and you're assigned an ID and password, giving you access to your private encryption key and the public keys of other users. These are all held on the public Xenophon server, but any encryption is carried out locally by the client software.

To send a message you logon to XenoMail and the software will automatically retrieve the public key of each recipient involved. These keys are themselves encrypted, then used locally to encrypt the message before sending it. Then, when the recipients get the scrambled message, they too logon to XenoMail and are sent their private key (again, in encrypted form) to de-crypt the contents and verify the sender.

Of course if they're not a XenoMail subscriber they can't do this which, on the face of it, implies that you can't send encrypted messages to someone until after they sign up. However, it is possible to create a read-only guest account for such recipients. They can then read messages you send, but if they want to encrypt their own they have to subscribe to the full XenoMail service.

It sounds complex and behind the scenes it no doubt is. In practical terms, however, XenoMail is simple and mostly transparent in operation. The encryption process is quick, even when logging onto XenoMail over slow dial-up lines, and we had no problems sending messages or un-scrambling those received. On the downside you can't encrypt Hotmail messages sent and received via Outlook. Neither can you use Microsoft Word as your Outlook editor, but those are minor niggles.

Admittedly it's not everyone who needs or wants to encrypt and digitally sign their e-mails. However, there are lots of business and individuals who do and they will find XenoMail an attractive proposition. It's cheap and easy, plus there's no need to invest in a complex PKI (Public Key Infrastructure) as with some alternative solutions. XenoMail also conforms to European and UK data protection legislation, and you can try it free for 60 days.

Public key encryption is good at keeping information private, but complex and expensive to employ. XenoMail removes these barriers by doing all the hard work on servers accessible by any registered user with the right client software. It's deceptively easy and worth investigating by anyone looking to protect their e-mail privacy.