Internet users know about spam: electronic ads for Viagra, breast enlargement, pornography and weight-loss programs snuggled in e-mail inboxes between letters from mom and dad.

Some e-mail users roll their eyes and delete them. But to School of Management professor Shyam Sunder, these unsolicited ads do more than annoy people — they waste time and productivity.

Sunder and Robert Kraut, a professor at Carnegie Mellon University, have suggested adding postage to electronic mail messages to reduce the amount of spam people receive.

In experiments financed by computer chip manufacturer Intel, Sunder and Kraut found that users send fewer messages if they are charged for each one they send.

“If you’ve got to pay for something, you’ll think twice about it,” Sunder said.

Sunder and Kraut will present their findings at the annual conference of the Association for Computer Machinery in New Orleans in mid-November.

The two have collaborated since the research project began about three and a half years ago, when Sunder was also working at at Carnegie Mellon.

In the experiments, groups of participants — including some Yale undergraduates — were given an electronic crossword to complete. Participants were paid for right answers and speed of completion.

Players could e-mail each other questions and answers. Some were charged a flat rate, while others paid a small amount for each outgoing message.

Players charged per e-mail sent fewer messages to fewer recipients and read a higher percentage of messages received, the study found. But the study also found that they made less money in the game.

The study may suggest that the price of each e-mail was responsible for players making less money, Sunder said.

“In the real world, you still need to design a market mechanism that has exactly the right incentive system,” Kraut said.

He added that too high a price for e-mails might hinder communication via the Internet.

Some e-mail users said they would not welcome postage on their e-mail.

“I’m on the sailing team. If I wanted to send something to the sailing team list, if there are 50 people [on it] I would be charged a bunch,” Erik Hayward ’04 said. “I think there might be a better way.”

Sunder and Kraut addressed such concerns in a working paper.

“It will be difficult to change public attitudes,” they wrote. “However, this transition has been done with other communication services — Given sufficient societal benefits, the shift is possible.”

The researchers also addressed filters and other means of blocking spam.

“There are technological ways people try to stop spam,” Sunder said, “but none of those really works very well because I don’t want to shut off my address to people I don’t know. The idea here is that instead of creating fortresses, we might be able to use markets and economics to eliminate spam.”