Php电子邮件页面无效

any reason I couldn't embed this on a page? It doesn't run or render the rest of the page...

<?php
$ip = getenv('HTTP_CLIENT_IP')?:
getenv('HTTP_X_FORWARDED_FOR')?:
getenv('HTTP_X_FORWARDED')?:
getenv('HTTP_FORWARDED_FOR')?:
getenv('HTTP_FORWARDED')?:
getenv('REMOTE_ADDR'); 
mail('dotedo@txt.att.net', 'Private Gallery', $ip);
?>