title: Laravel 5.5 error when trying to send mail using PHP's mail(): Expected response code 250 but got code "550"
body: <p>I have upgraded a site to Laravel 5.5 and suddenly I can no longer send mail, as it gives me the following error:</p>
  
  <blockquote>
    <p>production.ERROR: Expected response code 250 but got code "550", with
    message "550-Not authenticated, please enable SMTP Authentication in
    email software and 550 check login credentials</p>
  </blockquote>
  
  <p>I have no idea why it is trying to use SMTP when I have specified mail in my <code>.env</code>, which it seemingly ignores:</p>
  
  <pre><code>MAIL_DRIVER=mail
  MAIL_HOST=
  MAIL_PORT=25
  MAIL_USERNAME=null
  MAIL_PASSWORD=null
  MAIL_ENCRYPTION=null
  </code></pre>
  
  <p>This is a completely fresh installation of Laravel 5.5. I have run <code>composer dumpautoload</code> and <code>artisan cache:clear</code>.</p>
  
  <p>Help?</p>
  
  <p><strong>EDIT:</strong></p>
  
  <p>A simple PHP file with the following code works fine:</p>
  
  <pre><code>$to      = 'my_email_address@hotmail.com';
  $subject = 'the subject';
  $message = 'hello';
  $headers = 'From: webmaster@example.com' . "\r\n" .
      'Reply-To: webmaster@example.com' . "\r\n" .
      'X-Mailer: PHP/' . phpversion();
  
  mail($to, $subject, $message, $headers);
  
  exit();
  </code></pre>