title: How to stop e-mail clients from visiting links in e-mail automatically?
body: <p>I have a PHP script that sends out plain-text e-mails which contain links to certain actions like confirmations and agreements etc.</p>
  
  <p>What I have noticed is that the Web version of Outlook will automatically detect the link and visit the link in the background before the user clicks on it. I've noticed this because as soon as I open my e-mail, stuff changes in the database.
  Also checking the Apache access log, I see <strong>BingPreview/1.0b</strong> as the user agent.</p>
  
  <p>This is very bad as the user may not want to perform these actions.</p>
  
  <p>Are there e-mail headers that I can send to disable this behavior? Suggestions?</p>