Here are some reasons this may happen
• Spam or security filters – Spam or security filters scan incoming mail before delivering them to make sure there isn’t any malicious content. Our system automatically tracks clicks as opens, and we have no way of differentiating when a click is from a spam filter. This can sometimes lead to an unusually high number of opens from a single source.
• Email forwards – When your subscriber’s forward emails through their email client, any opens for the forwarded email are recorded as additional opens for your subscriber. Encourage subscribers to use the Forward to a Friend link instead to accurately track your opens.
• Email previewing – Most email clients have a preview window pane that will display when you select an email in your inbox list but without actually opening the email in its own window. Opens are track each time a user selects emails previewing up and down their inbox list.