Why cant my facebook email recieve email from unkown emails?

My facebook email (username@facebook.com) can receive email from known emails like from friends, but I tested myself, I cannot receive emails from UNknown sources, for example, I made a new gmail and sent a test email to my facebook email account. I did not receive it. I need to know how to receive these messages because it is vital for me, I have very important emails coming in and I cannot receive them. Please help fast!

Hello,

To modify who can send you Facebook messages and email:

-Go to the Account drop-down menu at the top of any Facebook page and select "Privacy Settings."
-Select "View settings" in the "Basic Directory Information" section.
-Change the setting for "Send me messages." Your options include Everyone, Friends and Friends of Friends.

Only emails from people that fall within the message privacy setting you choose will be delivered to your Facebook Messages. For example, if you select the "Friends Only" setting, you will not receive messages from email addresses that Facebook cannot confirm as belonging to one of your friends. Instead, those senders will receive automatic bounce-back replies.

Changes to the "Who can message me" privacy setting may take up to 24 hours to take effect.

With files from Facebook