How are email "Opens" determined?
When a recipient loads images, found within the email, NCR Customer Connect knows the images were loaded and counts it as an Open. 
  • An invisible image is embedded in each HTML email, this way if images aren't included in the email content, we are still able to track Opens.
  • If a recipient receives the plain text version of an email, we have no way of knowing the email was opened. 
For example, in some mail applications (ex: Outlook), users are set up to preview a message when they click once on an email and a double click opens the email message for a full review. If images are loaded, doesn't matter if it's a preview or full review, it counts as an Open.
Different mail clients act differently when it comes to loading the images, and users can often configure how or when or if they want to see images. So clearly more people could be viewing than you get credit for. This is the case with every application that track these events.