title: Outlook VSTO add-in HTMLBody does not contain signature on MailItem.Open event
body: <p>I've written an Outlook add-in that replaces a placeholder in the outlook signature file with a custom signature. In the NewInspector event I check to see if it is a mailitem and that it is unsent and if so hook up to the MailItem.Open event, which is where I replace the signature. </p>
  
  <p>Prior to Outlook 2016 version 1705 (build 8201.2102) that worked fine. Starting with that version when I check the HTMLBody in my MailItem.Open event the default signature is no longer there. Now on the MailItem.Open event for a new email, the body is always:</p>
  
  <pre><code>&lt;!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"&gt;
  &lt;html&gt;
  &lt;head&gt;
  &lt;meta name="Generator" content="MS Exchange Server version 16.0.8326.2033"&gt;
  &lt;title&gt;&lt;/title&gt;
  &lt;/head&gt;
  &lt;body&gt;
  &lt;!-- Converted from text/plain format --&gt;
  
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>If I revert back to version 1704, the code works again as expected.</p>
  
  <p>It's as though the signature is no longer being added to the MailItem.HTMLBody in the MailItem.Open event of new inspectors, but somewhere farther down the line. I've tried checking the documentation for any events that fire after the item is open and the default signature is added, but didn't see anything that looks like it would work.</p>
  
  <p>As a workaround for new emails I can test for the HTMLBody to be 239 characters, but that doesn't work for replies in an inspector, as it removes the details (from, sent, to, subject, etc.) of the original email, which are normally between the signature block and the original email. It seems those are no longer added on the MailItem.Open event either.</p>
  
  <p>I do the same things with inline responses via the explorer.InlineResponse event, which still works perfectly.</p>
  
  <p>My alternative is to update the actual signature files via the add-in instead of replacing them on the explorer and inspector events. The downside there is when I reply to a plain text email, my signature is plain text, whereas in the old setup even when replying to a plain text email my HTML signature would be included.</p>
  
  <p>Does anyone know of a different event I should be using for emails in inspector windows? Is this by design? Any other insights?</p>
  
  <p>Thanks in advance!</p>