Yahoo, which has marketed itself as a successful spam fighter for e-mail users, said most of the new functions are available only to subscribers of its Mail Plus service, which costs $29.99 a year.
The battle against spam has drawn the attention of e-mail providers and legislators, amid growing concern about the cost of junk e-mail to companies and consumers.
Yahoo said it has seen a 40 percent jump in spam from January to August and now averages 700,000 spam reports a day. Some analysts estimate that spam totals one-third of all e-mail, costing corporations billions of dollars a year.
