Yesterday Facebook changed the primary email address that users had signed up with. Without informing users first, a new facebook.com email address replaced previous primary email addresses for all users.
However, users can change the new email address back to their previous one. Computerworld Australia explains how:
To change the email address, a user should click on the “About” link on their main Timeline page, then click on the Edit button next to the “Contact Info” box. Although users can change which email address is shown on their Timelines, the facebook email address cannot be deleted, only hidden.
Read the entire article from Computerworld Australia here.