Problem with Mail() function

  
Hello Everybody,


    When I try to use mail() function it is not working.
This is my program:

<?php
$to="[email protected]";
$from="[email protected]";
$message="Hai\nHow r u?";
$subject="Hello";

$success=mail($to, $subject, $message, "From:$from");
if ($success)
echo "Your mail has been sent";
else
echo "There is some error";
?>

when I execute this, the output is
There is some error.

That means the mail is not sent.
So some please help me in getting this. The to address wahtever I gave is a valid address


It is urgent
 I thank u on beforehand

Please reply soon