Yahoo has been welcomed for its announcement to make users pay to use its email service, but claims have been made that it will be counter-productive.

The proposal was for a new paid mail service as a way to sidestep spam. The concept is that users purchase packs of 500 virtual stamps at a cost of $5 (£3), or one cent per stamp. Proceeds from the sales are then given to a participating charity selected by the user, and each of the email stamps carries the logo of the charity.

Yahoo is also hoping that the programme will cut down on spam, as by adding the unique stamp to each message, it is hoped that the email will breeze through spam filters.

Mark Harris, vice president of SophosLabs, claimed that the theory is sound up to a point, but then unfortunately it falls down badly.

Harris said: “The problem is that it is optional, and as soon as someone decides they don't want to opt-in, it won't work, because immediately users have to let through unpaid email and make the decision themselves.

“Another problem is that whilst pay-per-email would make it uneconomical for spammers, it would have the same effect on thousands of legitimate companies as well. Legitimate email marketing, newsletters, subscriptions to groups, even our own notifications about new malware campaigns would very quickly become too expensive and either the cost would have to be passed on or email would stop being used. If you had to pay for a letter to be delivered at your home, and you couldn't see what it was till you paid, the postal service never would have taken off.”