if(!filter_var($email, FILTER_VALIDATE_EMAIL))
или
if(!preg_match("/[-a-zA-Z0-9_]{3,20}@[-a-zA-Z0-9]{2,64}\.[a-zA-Z\.]{2,9}/", $email))
if(!filter_var($email, FILTER_VALIDATE_EMAIL))
if(!preg_match("/[-a-zA-Z0-9_]{3,20}@[-a-zA-Z0-9]{2,64}\.[a-zA-Z\.]{2,9}/", $email))
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