Function.mail error

I’ve used Weblogin to control user access to a website, but now on trying to use the "forgotten password" link, users get this error:

mail() [function.mail]: Policy restriction in effect. The fifth parameter is disabled on this system

This relates to line 108 in weblogin.processor.inc.php:

if (!ini_get(’safe_mode’)) $sent = mail($email, "New Password Activation for $site_name", $message, "From: ".$emailsender."\r\n"."X-Mailer: MODx Content Manager - PHP/".phpversion(), "-f {$emailsender}");

Could anyone tell me what change I need to make to remove the requirement for the fifth parameter (or another way to resolve this)?

Thanks