Yahoo Inc. is set to allow outsiders to create new services using the world’s most popular consumer e-mail program, in the broadest move the Web has yet seen to enlist independent programmers to build a company’s products for it.

Officials of the world’s largest Internet media company said on Friday it planned to give away the underlying code to Yahoo Mail, one of the crown jewels of its business, in a bid to encourage software developers to build new applications based on e-mail.

The move to open up the underlying code of Yahoo Mail — used by 257 million people — is designed to spark development of thousands of new e-mail applications built not only by Yahoo engineers but by outside companies and individuals.

Chad Dickerson, head of the Sunnyvale company’s software developer relations program, said he believed that the open approach to programming represented the biggest single Web software ever to be opened up for public development.

“Yahoo is a very large company but we can’t build every applications that a user might want,” Dickerson said in an interview at Yahoo headquarters. “You can imagine tens of thousands of niche applications (springing) from Yahoo Mail.”

Tags: Yahoo Mail, Code Giveaway, Web Software