Mailing queries are naturally only useful as on-site or embedded questions. You can use this question type, for example, to promote your newsletter. Alternatively, you can ask for the email address at the end of a survey to send your customers a voucher as a thank you for their feedback.
Our recommendation: The question should not be placed directly at the beginning or in the middle of a longer survey. Visitors are reluctant to provide their email address without added value. They are more likely to abandon your survey if you start immediately with the mailing request.