title: Sendmail host not found when running inside a docker container
body: <p>I am trying to send email from a docker container. The simplest one-liner I've been able to see is from an <a href="https://stackoverflow.com/a/45907529/4315597">earlier</a> stack overflow answer:</p>
  
  <pre><code>docker run --rm --net="host" php:fpm-alpine sh -c 'echo "Subject: test" | sendmail -v your@mail.com'
  </code></pre>
  
  <p>I change <code>your@mail.com</code> to my gmail address and run the command. The problem is that I now get this output in my terminal:</p>
  
  <pre><code>sendmail: recv:'220 mail.example.com ESMTP ready'
  sendmail: send:'EHLO linuxkit-025000000001'
  sendmail: recv:'250 mail.example.com'
  sendmail: linuxkit-025000000001: Host not found
  </code></pre>
  
  <p><strong>What do I need to do differently in order to get a simple sample mail to come through?</strong> </p>
  
  <p>I assume I'm close, since I'm getting output from sendmail.</p>