title: Outlook calendar conditional formatting based on customProp/itemClass
body: <p>I did not find a way to apply a conditional color formatting to appointments in Outlook Calendar based on customProperties or custom itemClass.  </p>
  
  <p>Here's what I did manage to do:  </p>
  
  <ul>
  <li><p>When I go to Outlook 2016 Conditional Formatting and select the Advanced tab, I can select the <code>Class</code> field and set the condition to contains <code>IPM.Appointment</code>. When applied this conditional formatting obviously works because all entries are of type <code>IPM.Appointment</code> :)<br>
  In the <strong>OfficeJS</strong> documentation it is said: "<em>You can create custom message classes that extends a default message class, for example, a custom appointment message class IPM.Appointment.Contoso.</em>" As the <code>Office.context.mailbox.item.itemClass</code> property seems readonly, where can I set such a class for my appointment?</p></li>
  <li><p>With <code>loadCustomPropertiesAsync</code> function, I can load and save custom properties for current item. This option seems pretty cool for what I want to do but I did not find a way to access it through any Outlook 2016 Conditional Formatting fields, any ideas?</p></li>
  </ul>
  
  <p>These were the 2 things I was thinking of, maybe you have an easiet way to do it in mind?</p>