Mail non envoyé avec php code

bonjour,

je suis débuatante sur la programmation php (send email with php) voici ma code php



<form action="mail2.php" method="POST">
<b>Email</b><br>
<input type="text" name="email" size=40>
<p><b>Subject</b><br>
<input type="text" name="subject" size=40>
<p><b>Message</b><br>
<textarea cols=40 rows=10 name="message"></textarea>
<p><input type="submit" value=" Send ">
</form>



<?php

/* All form fields are automatically passed to the PHP script through the array $HTTP_POST_VARS. */
$email = $HTTP_POST_VARS['email'];
$subject = $HTTP_POST_VARS['subject'];
$message = $HTTP_POST_VARS['message'];

/* PHP form validation: the script checks that the Email field contains a valid email address and the Subject field isn't empty. preg_match performs a regular expression match. It's a very powerful PHP function to validate form fields and other strings - see PHP manual for details. */
if (!preg_match("/\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*/", $email)) {
echo "<h4>Invalid email address</h4>";
echo "<a href='javascript:history.back(1);'>Back</a>";
} elseif ($subject == "") {
echo "<h4>No subject</h4>";
echo "<a href='javascript:history.back(1);'>Back</a>";

/* Sends the mail and outputs the "Thank you" string if the mail is successfully sent, or the error string otherwise. */
elseif (mail($email,$subject,$message)) {
echo "<h4>Thank you for sending email</h4>";
} else {
echo "<h4>Can't send email to $email</h4>";
}
?>



quand j'ai testé cette code sur le serveur directement ,l'erreur que s'affiche est que "Can't send email to $email".........
aide moi STP


merci d'avance