Sending an email to a Facebook user, knowing only his id

Question

If I send an email to john.doe@facebook.com then John will receive the message.

In my address book I have the Facebook ids of my friends.

Can I use those ids to send an email?
I just tried 12345@facebook.com and I received "Recipient address does not exist" (I replaced 12345 with my own Facebook id).

How to send an email knowing only the id?

Answer 1

You can send emails only to people who have usernames claimed. Facebook doesn't allow sending emails to IDs.

Below's my original (wrong) answer.

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Yes, the email is username@facebook.com. Your friends should receive them as long as you send them from an email associated with your Facebook account because the default setting is to accept messages from at least friends.

You likely didn't receive your test message because your setting is currently something restrictive. Emails to username@facebook.com are controlled by the same setting as all messages sent on Facebook, which is "Who can send you Facebook messages?" under How You Connect in Privacy Settings.

Answer 2

You can recover a user's facebook username through the Graph API. It is one of the few bits of data you can get on a user without them having authorized your application.

Visiting http://graph.facebook.com/FACEBOOK_ID will return a JSON object containing the username, their name, and anything else they leave open to the public.