email response

Those instructions are for Drupal 4.5. You need to add that line to the sites/default/settings.php file.
1. Add this line to the settings.php file:

$conf["smtp_library"] = "includes/phpmailer.inc";

2. Upload a file called phpmailer.inc into the includes directory. Modify it to your settings. Sometimes, you might not have to modify anything. If you don't have it, it looks like this:

include_once 'includes/phpmailer/class.phpmailer.php';

function user_mail_wrapper($mail, $subject, $message, $header) {
  $mailer = new PHPMailer();                 // instantiate a new mailer
  $mailer->IsSMTP();                         // send via SMTP
  $mailer->Host     = "localhost";     // SMTP server
  $mailer->SMTPAuth = false;                 // turn on SMTP authentication

//  $mailer->Username = '';          // SMTP username
//  $mailer->Password = '';          // SMTP password
  $mailer->AddAddress($mail);                // can only send to one recipient 
  $mailer->From     = 'noreply@example.com'; // from address (default root@localhost)
  $mailer->FromName = 'example.com';    // from name (default 'root user')
  $mailer->Subject  = $subject;
  $mailer->AddCustomHeader( explode("\n", $header)); // add custom header info
  // if body is not formatted properly change str_replace - see user.module user_mail() for details
  $mailer->Body     = $message;//str_replace("\n", "\r\n", $message); // Body of message
  if(!$mailer->Send()){
    watchdog('error', 'mail send error: ' . $mailer->ErrorInfo);
    return false;
  }
  return true;
}

3. Upload the latest phpmailer files from sourceforge.net into the includes/phpmailer directory. My directory has 2 files: class.phpmailer.php and class.smtp.php

4. If you are designing modules, make sure you send email via the user_mail function like this:

if (user_mail($email, $subject, $message, "")) {
  drupal_set_message("Your message was sent to ". $email);
} else {
  drupal_set_message("Your message could not be sent to ". $email, "error");
}