Zuckerberg said its new messaging platform will complement, not compete, with regular e-mail.
"This is not an e-mail killer," Zuckerberg said. "This is a messaging system that includes e-mail as one part of it."
Blogs had been buzzing with speculation about Facebook's changes, with a Facebook e-mail service being anticipated to compete with Google's Gmail.
Zuckerberg said Facebook's new e-mail service operates on three levels:
- It will combine all of the user's e-mails, texts and instant messages in one location.
- It will then store the entire history of conversations with each person.
- Finally, it will sort the user's inbox into priority folders created by that user.
"We would take all the conversations, all the messages that are being sent back and forth, and thread them together into one conversation between two people," said Andrew Bosworth, Facebook's director of engineering.
But in world of multiple e-mail addresses, not everyone is ready to add Facebook to their list.
"I have a Hotmail account and a Gmail account. I don't think I would sign up for a Facebook account," said Carrie Gumpert of Sherman Oaks. "I think I would just keep it simple."
Facebook officials insist users won't have to get a new e-mail address, but it will help, especially to receive messages from friends not on the social networking site.
"I have several accounts, but anything I do on Facebook could probably streamline it," said Yorba Linda resident Ellie MacColl. "I keep in touch with my kids through Facebook. I think it would be good."
Facebook will be rolling out the new service over the next few months by invitation only. All users should eventually be able to sign up.
Hotmail, followed by Yahoo then Gmail are the most used e-mail addresses.
With a half a billion users, Facebook could potentially change those rankings.
Zuckerberg unveiled Facebook's latest ventures from San Francisco, where he will also speak at the Web 2.0 Summit on Tuesday.
The Associated Press contributed to this story.