You might already use auto email sequences to communicate with your subscriber. The way it’s being done is preprogrammed. You send the emails at a certain pace, regardless of when and if at all they read them. That is not optimal.
At the end of each email have a call to action asking them to help you with just one click, something like: “Did you find this email message useful or enjoyable? Help me by simply clicking YES or NO.” The click will tell you two things: 1. They finished reading it. 2. If they liked it. You can use both to dynamically trigger the next email and also decide which email to trigger based on their reply.