title: Jenkins email notification is successfully sent but not received
body: <p>When I run test emails from the Jenkins configuration page they are reported as "successfully sent" but only sporadically arrive (sometimes after a long delay) to internal company email.  When I change the test email to send to an external (gmail) account it is immediately received.</p>
  
  <p>I am using the company smtp mail server.  I am able to telnet to it from Jenkins master and successfully send internal emails that way.</p>
  
  <p>Jobs notification emails never arrive even though Jenkins reports it as:</p>
  
  <pre><code>Email was triggered for: Success
  Sending email for trigger: Success
  Sending email to: &lt;MY EMAIL&gt;
  </code></pre>
  
  <p>I couldn't find anything in the jenkins.log (but maybe I need to look at a different log?).  Any help with troubleshooting the root cause would be great.</p>