SMTP error

i got a basic php script for mailing form data but it still isn't working.
This is the script:
<?
$name = $_REQUEST['name'] ;
$age = $_REQUEST['age'] ;
mail( "[email protected]", "Feedback Form Results", $age, "From: $name" );
?>
And this is the error:
Warning: mail() [function.mail]: SMTP server response: 550 5.7.1 Unable to relay for [email protected] in c:\Inetpub\wwwroot\action.php on line 4

Can anyone give any suggestion what i should do to make it work?