title: Security warning on custom Preview Handler
body: <p>I wrote my own preview handler on .NET for Outlook 2007/2010 and XP/Vista/Windows7</p>
  
  <p>When an e-mail with an attachment requires my handler to visualize it an alert says:</p>
  
  <p><em>"you should only preview files from a trustworthy source"</em></p>
  
  <p>I tried signing the EXE and the alert is still there.</p>