Why I'm getting an error like this - Warning: mail() [function.mail]: SMTP server response: 530 Relaying not allowed - sender domain not local in D:\INETPUB\VHOSTS\gaehambuilders.com\httpdocs\contacts.php on line 120 ?

Here is my php code,

if(isset($_POST['send']))

//if "email" is filled out, send email

{

//send email

$name=$_REQUEST['name'];

$email=$_POST['email'];

$cnum=$_REQUEST['cnum'];

$enq=$_REQUEST['enq'];

$email1=$_REQUEST['email'];

$to = "[email protected]";

$subject = "Test mail";

$message = "Hello! This is a simple email message.";

$from = $email1;

$headers = "From:" . $from;

mail($to,$subject,$message,$headers);

?>

alert ("Enquiry form submited successfully ! We'll get back you soon ");

Thanks in advance!