contacts not sending

<?php
// Contact subject
$subject ="$subject";
// Details
$message="$detail";

// Mail of sender
$mail_from="$customer_mail";
// From
$header="from: $name <$mail_from>";
$to ='admin@spotfindr.com';

$send_contact=mail($to,$subject,$message,$header);
if($send_contact){
echo "Thank you, your message has been sent!";
}
else {
echo "ERROR";
}
?>