Activity Log Shows Email Opened But No Email Sent

[PKM3328]

I'm wondering why there is a discrepancy in the activity log and what could be causing it. In 2 customers activity logs, it shows that they opened an email from a nurture. But theres nothing in the activity log showing that the email was sent. Any reasons why this is happening?

[SanfordWhiteman]

Sent Email logs are only kept for 90 days. Opens can occur far later, either by humans or by mail scanners.