PHP表单将电子邮件发送给多个收件人

我有一些PHP代码，用于将表单发送到特定的电子邮件地址.但是，我想在PHP发送时包含更多的电子邮件地址.我该怎么办？

<?php
if(isset($_POST['email'])) {
    // EDIT THE 2 LINES BELOW AS REQUIRED
    $email_to = "[email protected]";
    $email_subject = "MVP Nomination";

    function died($error) {
        // your error code can go here
        echo "We are very sorry, but there were error(s) found with the form you submitted. ";
        echo "These errors appear below.<br /><br />";
        echo $error."<br /><br />";
        echo "Please go back and fix these errors.<br /><br />";
        die();
    }
    // validation expected data exists
    if(!isset($_POST['username']) ||
        !isset($_POST['body'])||
        !isset($_POST['email'])) {
        died('We are sorry, but there appears to be a problem with the form you submitted.');       
    }
    $username = $_POST['username']; // required
    $body = $_POST['body']; // required
    $email_from = $_POST['email'];         // required
  $error_message = "";
    $email_exp = '/^[A-Za-z0-9._%-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}$/';
  if(!preg_match($email_exp,$email_from)) {
    $error_message .= 'The Email Address you entered does not appear to be valid.<br />';
  }
    $string_exp = "/^[A-Za-z .'-]+$/";
  if(!preg_match($string_exp,$username)) {
    $error_message .= 'The Username you entered does not appear to be valid.<br />';
  }
  if(strlen($error_message) > 0) {
    died($error_message);
  }
    $email_message = "Form details below.\n\n";
    function clean_string($string) {
      $bad = array("content-type","bcc:","to:","cc:","href");
      return str_replace($bad,"",$string);
    }
    $email_message .= "Name: ".clean_string($username)."\n";
    $email_message .= "Comments: ".clean_string($body)."\n";

// create email headers
$headers = 'From: '.$email_from."\r\n".
'Reply-To: '.$email_from."\r\n" .
'X-Mailer: PHP/' . phpversion();
@mail($email_to, $email_subject, $email_message, $headers);  
}
header("Location: ThankYou.html");  //Redirect to Thank You HTML page after email is sent
?>​

谢谢。