Yahoo opens up e-mail APIs to outsiders.

Yahoo on Wednesday is expected to release software that will allow third-party developers to write applications using Yahoo Mail.

The move to open up the application programming interfaces (APIs) to Yahoo Mail is meant to encourage Web developers to build applications that use the mail service. The company expects these third-party "mashups," hybrid software that combines content from more than one source, will bring in more customers.

"There is tremendous potential for additional usage of Mail. By providing more user experiences, we believe we will increase engagement and utilization of the platform," said John Kraemer, vice president of Yahoo Mail.

Yahoo is also providing financial incentive to developers, offering $10 for every new Yahoo Mail premium account that third parties bring in during a trial period.

The APIs will be available either via the Simple Object Access Protocol (SOAP) or JSON, a JavaScript-based method.

One new application that was built by an outside developer creates a connection between Yahoo Mail and Yahoo's Flickr photo-sharing site.
Each time a new e-mail comes in, the service looks at the subject line and retrieves a photo from Flickr based on the words of a subject line. E-mail pertaining to a trip to France, for example, could automatically generate photos of the Eiffel Tower, explained Chad Dickerson, senior director of the Yahoo Developer Network.

Over the past two years, Yahoo has made efforts to reach out to Web developers. It first discussed opening up its Mail APIs last fall, Dickerson said.

By providing APIs to its services, Yahoo, like other Web companies, hopes to drive traffic to its services and build a rich third-party network of add-on products.

Yahoo Mail has about 250 million users. Separately, Yahoo announced Tuesday that it will give its Mail users unlimited storage beginning in May.