Why does my activity log say "email opened" or "SmartSender link opened", but the recipient never opened the email?

There are some rare instances where the activity Email Opened or a notification for a SmartSender Link or SmartSender Resource Opened may be falsely triggered. If the contact or recipient claims that they have never opened or received your email/resource, when the PhoneBurner activity says otherwise, it's possible that their email client may have used a spam filter or virus scan to detect for malicious activity or potential phishing. This may appear as a Email Opened flag to our service, and could lead to a false Email Opened activity/notification.

This is completely dependent on the recipient's email client as some anti-virus programs follow the links in the email to see if they can determine if the link goes to a phishing site. When they do the aforementioned, the link is counted as clicked and the email may appear to have been opened.