Hiya,
Once I have closed NPS survey, I know I can see those emails addresses that bounced or were unsubscribed. However I do believe that is more useful to get that info while the survey is still active. In this way I could manage to get a different customer´s email address and send to that address the same NPS. I don´t want to wait to get this info for the next NPS that in my case it could be 3 months later.
Thanks