Currently if a user sends for the first time an email to the support address, a ticket will be generated under a new user. This user will have the email address unverified, and hence you won't be able to send a NPS survey after closing the case.
Given that one can mark a user's address as verified using the API, it would be great to have an option to mark all incoming email addresses as automatically verified, since almost all incoming tickets are from rightful addresses.