title: Email with nodemailer fails on Heroku
body: <p>In my node.js-App, that runs on 1 Heroku worker, needs to send out emails from time to time. The logic is the following:</p>
  
  <pre><code>var transporter = Email.createTransport({
      service: 'yahoo',
      auth: {
          user: process.env.CRAWLER_MAIL,
          pass: process.env.CRAWLER_PWD
      }
  });
  transporter.sendMail({
                              from: process.env.CRAWLER_MAIL,
                              to: process.env.CRAWLER_RCVR_MAIL,
                              subject: 'subject',
                              text: 'text'
                          }, function(err, result) {
                              if (err !== null) {
                                  console.log(err);
                              } else {
                                  ...
                              }
                          });
  </code></pre>
  
  <p>I tested this with <code>foreman start</code> and it worked fine. Nonetheless, once deployed to Heroku, the transporter always emits an error with status code '564  :  We were unable to deliver your message. Please try resending your message by adding some text.'</p>
  
  <p><code>process.env.</code> hold the correct values, I checked for that, and <code>text</code> is always a string. </p>
  
  <p>What could be wrong? </p>