title: Set CustomProperties on appointment for all attendees
body: <p><strong>tl;dr</strong></p>
  
  <p>When setting <code>CustomProperties</code> to an appointment that has attendees, only the appointment for the organizer gets the <code>CustomProperties</code>. The properties do not propagate to the appointments of the other attendees. </p>
  
  <hr>
  
  <p><strong>Longer version</strong></p>
  
  <p>When we create an appointment with multiple attendees and then log in as each attendee, we notice that each <code>ItemId</code> is different. So, it appears that each attendee in a meeting gets their own copy of an appointment. (Would really like someone to confirm this is true).</p>
  
  <p>However, when setting a custom property from our add-in (using the Outlook JavaScript API), only the organizer's appointment gets the custom property as we are unable to see the custom property when we log in as any of the other attendees.</p>
  
  <p>Snippets from our code that is relevant:</p>
  
  <pre><code>Office.initialize = function (reason) {
      $(document).ready(function () {
           Office.context.mailbox.item.loadCustomPropertiesAsync (onCustomPropertiesLoaded);
      });
  };
  
  function onCustomPropertiesLoaded(asyncResults) {
      _customProps = asyncResults.value;
  }
  
  //Set custom properties
  _customProps.set("myProp", "true");
  _customProps.saveAsync(customPropertiesOnSaved);
  </code></pre>
  
  <p>Is there a way to have each copy of the appointment have the custom property?</p>