Mail() function not sending the email..please help!

I have tried to upload it to two different servers but I get nothing…

here is the code Im using:

<?php
$to = "p_mail@yahoo.com";
$subject = “Email”;
$firstname = $_REQUEST[‘firstname’];
$surname = $_REQUEST[‘surname’];
$company = $_REQUEST[‘company’];
$email = $_REQUEST[‘email’];
$message = $_REQUEST[‘message’];
$headers = “From: $email”;

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

if($sent) {
print “sent!”;

} else {
print “error!”;
}
?>

…I get the “sent!” message but thats it, no email comes through…