"We don't think that a modern messaging system is going to be email," said Mark Zuckerberg, who was widely expected to introduce an email system at Facebook's press conference today. Instead, the Facebook  CEO was clear: "It's not email," he said. "It's a messaging system that includes email as a part of it."
What does that mean? Zuckerberg explained that unlike email (which has too much "weight and friction" from subject lines, addresses, etc.) Facebook's system, which will begin as invite-only and be rolled out over the next few months, will be seamless, informal, immediate, personal, simple, and minimal. Here are the three major features that distinguish Facebook's platform from regular old email.
"This system is definitely not email," reiterated Andrew Bosworth , director of engineering at Facebook. "We modelled it after chat."
Facebook's messaging system is different than any other email service (namely, Gmail) in that it doesn't just collect email. Texts and SMS, IMs and chat, emails and Facebook messages--"they don't work that well together," explained Bosworth.
Now, they'll all be assembled into one thread, blurring the lines of what an "inbox" is. So, rather than having your texts stored on your phone, and your IMs stored on iChat, and your emails stored on Yahoo, Facebook will compile your messages into one place.
Additionally, Facebook will offer users an @Facebook.com email address, but it's not necessary to use the system.
Related to seamless messaging, Bosworth complained that messages are "not in one place." Until now. Facebook will organizes all your messages with friends in one place, and provide a detailed overview of your conversation history across any platform.
Users can scroll through entire conversation histories with their boyfriends or girlfriends, and see all types of messages--texts, emails, etc.--in chronological order. It's a stream of conversation--not a thread.
"It's always a problem when I see a message from my mom and it's sandwiched between a bank statement and a bill," said Bosworth. "By default, you're going to see messages from your friends and their friends only."
On Facebook's system, the messages are entirely aimed at the social graph: messages are divided between messages with friends, other messages (say, a friend that you don't give as much attention to as your best friend), and junk.
"These are conversations with the people you care most about, no matter what device or what medium you want to use," Bosworth said.
"This is not an email killer," Zuckerberg concluded. He said the wide ranging reports of Facebook introducing a "Gmail killer" were over-dramatic. "We don't expect anyone to say, I'm going to shut down my Yahoo or Gmail account and switch exclusively to Facebook," he said. "We don't think that's what's happening in the world."
But that's not to say it won't happen eventually.
"Whether it's one day in six months, or a year, or two years," the Facebook CEO said, "this is the way the future should work."