Facebook changed users' email addresses and forced them to use new emails ending with @facebook.com.
However, here are easy steps for reverting back your email address on Facebook.
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1) Go to your profile
2) Click "Update Info"
3) Click the "Edit" button in Contact Info section
4) Edit box with original and @facebook.com email address will appear. Here, you can change who can see your e-mail address and which e-mail addresses they can see.
5) Click on the circle along from the @facebook.com address