title: How to enable error In Nodemailer if email is not exist
body: <p>nodemailer :  "^2.4.2"</p>
  
  <p>I am sending mail using nodemailer. It's working fine. But while using not existing email, I am not getting any error: </p>
  
  <p>I have code as;</p>
  
  <pre><code>exports.sendMail = function (req, resp, reqBody, callback) {
      var smtpTransport = nodemailer.createTransport(settings.smtpConfig);
      var data = JSON.parse(reqBody);
      var mailOptions={
          to      : data.toAddress,
          cc      : data.ccAddress,
          bcc     : data.bccAddress,
          subject : data.subject,
          html    : data.message
      }
      smtpTransport.sendMail(mailOptions, function(error, response){
          if (error) {
              callback(null, error);
          }else{
              callback(response);
          }
      });
  };
  </code></pre>
  
  <p>So if i use any not existing email Id it doesn't throw any error;</p>
  
  <p>For eg:If I send toAddress as 'dummy@gmail.com' -- it doesn't throw any error.</p>
  
  <p>I got response as </p>
  
  <pre><code>{ accepted: [ 'dummy@gmail.com' ],
    rejected: [],
    response: '250 2.0.0 OK 1466501212 23sm18003603qty.40 - gsmtp',
    envelope: { from: '', to: [ 'dummy@gmail.com' ] },
    messageId: '1466501201867-84b63b27-ce337819-b06c739f@localhost' }
  </code></pre>
  
  <p>Same case for cc also.</p>
  
  <p>Any help appreciated.</p>