Sarah Sands: The first rule of emailing: send it and be damned

We don't know whether police investigating cash for honours will discover anything criminal as they go through the emails they have been recovering from the "Delete" queue in Downing Street. If they do, it will show astonishing naivety on the part of the emailers. I thought anyone who'd seen Prime Suspect knew that your mobile phone signal could put you at the scene of the crime, that we leave DNA wherever we go, and that fingerprints are unique. What will dumb criminals do next? Try polonium as a murder weapon because no one can trace it?

I have never properly understood the technology of the internet, but I have learnt the first principle, which is that you don't write anything in an email that could ever embarrass you. There is no such thing as a deleted email, and yet we dash off an email with a carelessness we would never use in a letter. It feels nearer to speech than to writing. How treacherous that little delete instruction is, with its implicit promise that the email will vanish.

Some of the consequences are merely farcical: the gossip about a friend that we inadvertently sent to the subject of it. The bawdy or cutesy exchange between lovers that is suddenly read and derided by every office worker on the planet. The desperate damage limitation exercise as the emailing victim tries to plead irony.

But other email mistakes have more serious consequences. If I were an international terrorist I would take great care never to write "bomb" in an email, for the British and US security services can scan millions of emails a day and pluck out anything containing words they don't like. And if I were a young man in an office, I would hesitate to describe my intentions towards the comely new temp because I couldn't be sure that the lawsuit- conscious bosses hadn't installed an anti-sexism programme.

At one office I worked in, most of the staff assumed that all emails were monitored. My suspicion was aroused by a boss who refused to commit anything to email. As our relationship became more uneasy, I would taunt him by firing off emails starting: "Could I be clear about what you meant during our last conversation..."

The investigation into the Downing Street emails may not determine the guilty and the innocent so much as the responsible and the irresponsible.

The unique horror of emails is the simplicity of sending them and the fiendish complication of retrieving them. I remember dashing round to a colleague's desk, luring them away and then opening and deleting the message I had sent by mistake. Usually, it is beyond salvation and you just have to put up with the mournful, reproachful gaze from across the office.

Ruth Turner, Tony Blair's senior adviser, is described by those who know her as friendly, informal, trusting, unpolitical. In other words, an emailing catastrophe waiting to happen.

Before our fingers dance across the BlackBerry keyboard with our unconsidered thoughts and jokes and erratic punctuation, we should imagine the recipient as a lawyer rather than a friend.

I remember Barbara Amiel informing me gravely that years of correspondence between us, when she was a columnist and I was her editor, was now in the hands of big-shot corporate lawyers. Obviously, I had never written: "Let's rob a bank." It was worse than that. I realised that I must have been oily, ambitious, gushing, boastful and indiscreet during that period, and it would all come to light.

Emails are a technological hoax. We have loved them for being private when all the time they were indicting, humiliating and wholly public.

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