เพิ่งเขียน php ค่ะ พอเอาขึ้น server แล้วมีปัญหาค่ะช่วนหน่อยนะค่ะ Fatal error: Class 'Mail' Warning: include_once(Mail.php) failed to open stream: No such file or directory

<?php
include('Mail.php');

/**
 * Send mail using PEAR Mail Factory
 */
function drupal_mail_wrapper($mailkey, $to, $subject, $body, $from, $headers) {
    $headers['From']     = $from;
    $headers['To']        = $to;
    $headers['Subject']    = $subject;

    $params['host']     = ini_get('SMTP');

    $smtp =& Mail::factory('smtp', $params);

    $mail = $smtp->send($to, $headers, $body);
    if ( PEAR::isError($mail) ) {
        watchdog('debug', $mail->getMessage());
        return false;
    }
    else {
        watchdog('debug', 'Mail successfully sent!');
    }
    
    return true;
}
?>