What automation can generate reports on subscribers' engagement with marketing emails?

The correct choice highlights the ability to generate reports specifically related to subscribers' engagement with marketing emails. Reports like the Engagement Activity Report are fundamentally designed to provide insights into how subscribers interact with various marketing efforts, including email campaigns. These reports can track metrics such as opens, clicks, and other forms of engagement, which are vital for assessing the success of email marketing initiatives.

The other options, while they focus on different aspects of subscriber management, do not primarily serve the purpose of reporting on engagement levels. For example, the Unsubscribe Event Extract would specifically focus on tracking those who opted out of receiving emails, which does not provide insights into how remaining subscribers engage with the content. Similarly, Complaint Tracking Extract is focused on identifying and analyzing complaints related to marketing efforts rather than engagement metrics. Lastly, the Journey Engagement Summary, while it may touch on engagement within a specific marketing journey, does not concentrate solely on overall email engagement metrics across all campaigns.

Thus, the Engagement Activity Report stands out as the most relevant choice for generating comprehensive insights into subscribers' engagement with marketing emails.