How do I enable the feature that warns me if I try to send an email message without a subject line? Does such a feature exist?

The feature you describe doesn't exist, but you can use Outlook 2002 or Outlook 2000 Visual Basic for Applications (VBA) code to create it. Take the code that Listing 1 shows and place it in Outlook VBA's built-in ThisOutlookSession module. The Application_ItemSend event handler will display an alert if you try to send a message with a blank subject line.