Yahoo Inc. (YHOO), the world's largest consumer e-mail provider, on Monday said it has embedded instant messaging features inside its e-mail program, bridging a generational divide that has confused many users.

Heavy Internet users, especially younger, Web-savvy users of social networking sites or office workers, have long toggled between e-mail and instant messaging services.

But for more occasional users of consumer e-mail services, the allure of instant messaging has remained far from obvious.

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Consumers can now run the two programs in one Web browser. There is no need to download Yahoo Messenger software, a complication for users who are not technically inclined.

Each instant messaging dialogue will take place in a new conversation window within Yahoo Mail, allowing people to chat with multiple friends simultaneously, without leaving e-mail.

John Kremer, vice president of Yahoo Mail, said in a phone interview embedding instant messaging makes e-mail "an even more social experience" — by transforming how one communicates from a letter-writing experience into a back-and-forth chat.

"We are hopefully bridging the gap between e-mail users and IM users," Kremer said. "There is still a chunk of Yahoo Mail users who aren't using IM."

Yahoo is in effect moving the mountain of its 250 million Yahoo Mail users by eliminating the elusive technical distinctions that have separated the two modes of communication and limited the appeal of instant-messaging among many users.

To guard against overwhelming its network, Yahoo plans to steadily upgrade all Yahoo Mail users in coming months.

Yahoo is not the first to blend the immediacy of instant message with the greater depth allowed by e-mail communications: Google Inc. (GOOG) incorporates its Google Talk messaging system inside its G-mail program, while Microsoft's (MSFT) e-mail service alerts a user when e-mail recipients are also on instant messaging.

It then allows the user to send messages to either e-mail or instant messaging recipients.

"By allowing users to jump between the two modes of communication, we are laying the groundwork for other types of communications," Kremer said, referring to features like Web phone-calling that are already part of many IM services.