更改php-pear-mail中的电子邮件标题

我正试图弄清楚如何使用谷歌的SMTP服务器从php发送电子邮件，但要更改from标头以匹配我的域。电子邮件发送良好，但收件人看到它是从myemail@gmail.com而不是me@mydomain.com.我正在使用php-pear邮件发送。

require_once("Mail.php");
$from = "Me <me@mydomain.com>";
$to = "Zach <myemail@gmail.com>";
$subject = "Hi!";
$body = "Hi,'n'nHow are you?";
$host = "smtp.gmail.com";
$username = "****";
$password = "****";

$smtp = Mail::factory('smtp',
array ('host' => $host,
  'auth' => true,
  'username' => $username,
  'password' => $password));
$headers = array ('From' => $from,
  'To' => $to,
  'Subject' => $subject);     
$mail = $smtp->send($to, $headers, $body);

if (PEAR::isError($mail)) {
    echo("<p>" . $mail->getMessage() . "</p>");
} else {
    echo("<p>Message successfully sent!</p>");
}