There is a potential reason why this happens:
- The recipient of your email hasn't downloaded pictures (e.g. Outlook) or displayed images (e.g. Gmail) when opening your email. Pictures must be downloaded or images displayed for ContactMonkey to track opens. Also it would be helpful if you inserted an image into your email signature to increase your open rates. You can read how to do this here for Outlook and here for Gmail.
However, ContactMonkey tracks the clicks of links in your emails with 100% accuracy regardless of whether the recipient downloads pictures or displays images. You can learn more about link tracking here.