Washington, Nov 19: When it comes to preventing unwanted emails in the inbox the answer might lie in mathematical puzzles like Sudoku.

Australian computer scientist Paul Gardner-Stephen from Flinders University in Adelaide is searching for ways to improve the existing spam filters, which he says are not very efficient.

"The trouble is that they're not entirely accurate, so you still get some spam in your inbox and some real mail gets bounced," ABC online quoted him, as saying.

Gardner-Stephen came up with the idea to add an automatic system, to the existing filters, which would require mail servers to solve a mathematical puzzle if they want their mail to reach you. He is due to describe the system at a meeting of the Institute of Electrical and Electronics Engineers this week.

He explains how the mail server computer that receives your email would use an existing spam filter to decide how likely it is that an incoming message is spam and that if it looks suspect, the server would automatically respond to the sending server with a mathematical challenge to solve before the message is delivered.

Once the spam filter is certain that the message is junk, the puzzle would be harder to solve.

For messages that are clearly spam, the puzzle could be set to take about an hour to solve, Gardner-Stephen says.

"If someone's trying to send spam, they end up with a lot of puzzles to solve, so they can only send relatively few messages a day," he says.

In technical terms, the system is known as a 'proof-of-work' scheme. By providing a solution to the puzzle, the sending mail server is proving that the message is important enough for it to do a certain amount of work.

"Sudoku is a good example of the kind of puzzle," Gardner-Stephen says. "It's easy to verify you've got it right, but not easy to do."

So far, the system only exists in theoretical form, but Gardner-Stephen is planning to try a test on a single mail server within the next year.

If all goes well, it might take 5-10 years for a system like this to be adopted across the many thousands of mail servers across the internet, he says.

He also publishes his paper on the arXiv website. (ANI)