That way you can get false positives unless you concatenate using a non-valid character in the protocol foo@example.com other@example.net foo@example.co mother

That way you can get false positives unless you concatenate using a non-valid character in the protocol foo@example.com other@example.net foo@example.co mother@example.net Btw, storing just the domains, or inverting the email strings, would have speed up the comparison