Spam could prove cripplingly expensive for companies whose staff use a wireless internet connection that charges for the amount of data received, such as those using a GPRS cellphone link. The answer, says Nihon Digital of Tokyo (GB 2382190), is for every user to have several email addresses, only one of which is published. If mail arriving at the published address comes from a source on an 鈥渁pproved鈥� list, it is sent straight through to the wireless appliance.
All other mail is shunted to a secret address, where a server checks whether other people are receiving similar messages. If they are, the message is likely to be spam and is deleted. Any messages that are not duplicated in this way are deemed legitimate, even if they come from an unknown address, so the server resends them from an artificial email address that is on the mobile computer鈥檚 list of trusted senders.
