In February 2011, Facebook rolled out a new messaging platform that integrated standard Facebook messages and real-time Facebook chat messages into a single inbox. Also included in this new package is an "@facebook.com" email address for each user, which enables even non-Facebook users to send messages to a Facebook user's email inbox. If you know someone's Facebook username, send a message to his Facebook inbox from an outside email address.
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Visit the Facebook profile of the friend you want to message. Click your mouse inside your browser's address bar and highlight the text which appears after the main Facebook URL -- this is your friend's Facebook username. Copy it to your clipboard.
Create a new email message. Paste your friend's Facebook username into the "To" field and type in "@facebook.com" after it.
Enter a message subject and text as you would with any other email message. Proofread your message to make sure it reads exactly as you want, then click "Send."