PHP: what's wrong here?!

<?
$msg = "E-mail sent from Xtrasensory

";
$msg .= "From Name:    $sender_name
";
$msg .= "From E-Mail:  $sender_email
";
$msg .= "Telephone:    $telephone

";
$msg .= "Message:      $message

";
$to = "[email protected]";
$subject = "Visitor at Xtrasensory.net";
$mailheaders = "Sent from my website 
";
$mailheaders .= "Reply-To: $sender_email

";
mail($to, $subject, $msg, $mailheaders);
?>

it’s all set up and ready to go but I don’t receive any emails…hmmm