title: How do you normalize an email address in PHP?
body: <p>Is there a function in PHP that can normalize an email address?</p>
  
  <p>E.g., if case isn't significant, then <code>FOO@example.com</code> -> <code>foo@example.com</code>.</p>
  
  <p>I don't know the rules for when email addresses should be considered "the same", so I don't want to implement this myself.</p>