Is this PHP contact form secure?

Can you please tell me whether the following PHP contact form is secure? (It gets used with AJAX.)

<?php
$email_to = "myaddress@email.com";

$email_subject = "My subject";

$name = $_POST["name"];
$email = $_POST["email"];
$message = $_POST["message"];

$error_message = "";

$email_message = "Form details below.\n\n";

function clean_string($string) {
  $bad = array("content-type","bcc:","to:","cc:","href");
  return filter_var(str_replace($bad, "", $string), FILTER_SANITIZE_EMAIL);
}


$email_message .= "Name: ".clean_string($name)."\n";
$email_message .= "Email: ".clean_string($email)."\n";
$email_message .= "Message: ".clean_string($message)."\n";


// create email headers

$headers = "From: myaddress@email.com\r\n".
           "Reply-To: myaddress@email.com\r\n".
           "X-Mailer: PHP/" . phpversion();

@mail($email_to, $email_subject, $email_message, $headers);  

?>