Recently I wanted to register a new Facebook account, using the address info_AT_alfanhendro.com . However when submitting it to Facebook it says ‘Please enter a valid email address” . Upon some searching, apparently the reason is due to Facebook restricting certain generic word for the prefixes. After changing to another email address, it works.
Here is some information from a Facebook page about the error message “Please Enter A Valid Email Address”
Unfortunately we do not support email addresses with generic prefixes (e.g. info@, webmaster@, etc.). Since email addresses of this nature are typically used for organizations and businesses, we do not allow them to be used for personal Facebook accounts. You will need to use a personal email address that does not contain this type of prefix. There are no exceptions to this rule.