title: Slack API - Post message via user email
body: <p>I need to send a message to slack user but have only the email address of the user. </p>
  
  <p>Does Slack API provide such functionality?</p>
  
  <p>Any idea/workaround is really appreciated!</p>
  
  <p>Edit:
  I need to send a slack message from jenkins, according to the build state. Jenkins Slack Plugin does not provide such functionality as far as I am aware, so I'm trying to do that directly calling Slack API from jenkins shell.</p>