I have installed LimeSurvey and created a survey for our customers. After that I copied the link and paste it in your trigger in Zammad which is sending a mail on closed state tongue customer.
You can define a separate trigger if you want.
Now you can use tags to track the voting. Our trigger send one mail per customer based on the tag.
Limesurvey is free software and has a good live reporting. So we can see live the results of our survey.
