Facebook has ramped up competition with AOL, Yahoo, Microsoft and Google with a product to rival their email services.
Facebook Messages aims to tie users more closely to the social networking site at a time when everyone is battling for their attention.
The product will merge texts, online chats, and emails into one central hub.
Facebook said traditional email is too slow and cumbersome and needs to step into the modern world of messaging.
"This is not an email killer," Facebook co-founder Mark Zuckerberg told reporters and analysts at an event in San Francisco.
"Maybe we can help push the way people do messaging more towards this simple, real time, immediate personal experience. Email is still really important to a lot of people. We think this simple messaging is how people will shift their communication," added Mr Zuckerberg.
'Killer app'
In a case of bad timing, reports surfaced hours after the Facebook launch that Gmail suffered an outage.
The new service is seen as offering an alternative to Gmail, the fastest growing web service in the past year with over 193 million users according to data tracker ComScore.
The irony was that ahead of the announcement, speculation was rife that Facebook's new product would be most crippling for Gmail. Mr Zuckerberg said he did not see it that way.
"In reality they have a great product.
"We don't expect anyone to wake up tomorrow and say 'I'm going to shut down my Yahoo Mail or Gmail account'.
"Maybe one day, six months, a year, two years out people will start to say this is how the future should work," said Mr Zuckerberg.
AOL which at the weekend previewed changes to its once popular web mail service disagreed email is doomed.
"Email remains one of the killer apps on the internet," said Brad Garlinghouse, AOL's senior vice president of consumer products.
Industry analyst Augie Ray of Forrester agreed.
"Research we have done shows we know that in the US 90% of adults check their mail at least once a month and 59% of adults say they maintain a profile on a social networking site.
"There is a big gap between the reach social media has and the reach email has."
Ease of use
At the heart of Facebook Messages is an effort to ensure users "see the messages that matter".
The new feature will simplify how people communicate whether it be via text, instant messages, online chat or email. All these messages will come into one feed known as a social inbox allowing users to reply in any way they want.
Facebook said around 70% of users regularly use it to send messages to friends and and that a total of four billion messages pass across the site every day.
"We really want to enable people to have conversations with the people they care about," Facebook's director of engineering Andrew "Boz" Bosworth told BBC News.
"It sounds so simple. We have all this technology that should be enabling that but it's not. It's fragmenting that. So I have one conversation on email with my grandfather and another with my cousin on sms and all these things don't work the same way.
"I shouldn't have to worry about the technology. I should just have to worry about the person and the message. Everything else is just getting in the way," added Mr Bosworth.
The new system will be modelled more on chat than traditional email which means there will be no subject lines, cc or bcc fields.
Liz Gannes of technology blog AllThingsD said she believed users will have a bit of a learning curve on their hands.
"I think the product is just different enough from what people are used to that it will feel really weird to users for a while.
"The lack of subject lines will get people upset at first and then of course they will probably realise they never wanted them anyway."
'Game over?'
Other features include being able to store conversations so users can have a complete archive of communications with friends and family. Mr Bosworth likened this to a modern day treasure trove of letters stored in a box.
Incoming message will be placed in one of three folders - one for friends, another for things like bank statements and a junk folder for messages people do not want to see.
The product will also represent a challenge to Yahoo with over 273 million users and Microsoft which has nearly 362 million.
"For me today represents the day when Facebook truly becomes a portal on the level of Google, Yahoo, Microsoft and AOL," Charlene Li social media analyst with the Altimeter Group told BBC News.
"They now have to start making their inboxes more social. Friends are the new priority as opposed to the conversation. This makes Facebook so much more functional."
Robert Scoble technology writer and founder of Scobleizer.com said this product gives everyone something to aim for.
"This is a new kind of communications system but its not game over for Yahoo and Gmail and all the others because it will take decades to get people to stop doing traditional emails.
"However this is something new and very powerful because Facebook can tap into my social graph and ensure that only my friends are there and I won't get spammed."
Facebook said this product was the biggest the social networking giant had worked on to date.
The company will also offer an @facebook.com email address to every one of its more than 500 million users.
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