title: Powershell string does not contain
body: <p>I have some code that takes in a string,</p>
  
  <pre><code>Foreach($user in $allUsers){
      if($user.DisplayName.ToLower().Contains("example.com") -or $user.DisplayName.ToLower()) {
      } else {
          $output3 = $externalUsers.Rows.Add($user.DisplayName)
      }
  }
  </code></pre>
  
  <p>Part of the <code>if</code> right after the <code>-or</code> I need to check if the string does not contain an @ sign. How can I check to see if the @ sign is missing? </p>