Display question based if customer is not part of a contact list

While sending emails, ensure you have the necessary variable.. Then create the same variable in the survey flow. Use that variable to display that question

Hi,

You could also add a web service element to your survey flow and leverage the “search directory contacts” API with multiple filters, for example “email” and “inList”, and then apply logic based on the answer you receive.

See https://api.qualtrics.com/c79e78a949572-search-directory-contacts