Facebook has devised an interesting and people-centric approach to fighting spam.
By giving out @facebook.com email addresses to all users, the company could have opened up potentially disastrous issues with spam. The first part of a users’ email address is their vanity URL address or http://www.facebook.com/name. Because those URLs are crawlable, that means bots will easily be able to find millions of email addresses to spam.
However, Facebook is confronting this by using the social graph — only people who are a user’s friends or friends of friends can e-mail them.
If a person not connected to a user e-mails them, it will go to the ‘Other’ part of the inbox. If they find those messages important, they can move them from that folder into the main part of the inbox. From then on, they’ll get all emails from that person immediately.