title: Url protocol handler security warnings
body: <p>I have a custom url protocol handler for urls of the form myhandler://path/to/something.  This is registered to a locally installed client application that handles the requests and does "the right thing".</p>
  
  <p>However, when I have a link of that form in outlook (2007), outlook displays a big scary warning that says:</p>
  
  <blockquote>
    <p>Microsoft office has identified a potential security concern</p>
    
    <p>This location may be unsafe
    ...</p>
    
    <p>Hyperlinks can be harmful to your computer and data.  To protect your computer, click only those hyperlinks from trusted sources.</p>
    
    <p>Do you want to continue?</p>
  </blockquote>
  
  <p>I am aware of the outlook registry key that would enable me to disable these warnings entirely (<a href="http://support.microsoft.com/?kbid=925757" rel="noreferrer">http://support.microsoft.com/?kbid=925757</a>), but I don't want to be a "bad citizen" on the machine.</p>
  
  <p>Is there some way that I can "whitelist" my url protocol handler to indicate that I have done due security diligence without opening up access to other URL protocol handlers on the machine that might not be hardened to malicious user input?</p>
  
  <p>Outlook does not prompt for URLs of the form <code>http:</code> <code>https:</code> <code>mailto:</code> (and perhaps others).  Is this list hardcoded somewhere deep in the bowels of office or is there some way to add my specific protocol to the list?</p>