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For automated respondent identification you have to use the Email/List Management system. When you schedule email delivery through this system, every email address is uniquely identified and coded. This enables the identification of who has taken the survey and who has not. The email address is saved with the Response and is available in the Response Viewer and also with Excel and CSV downloads.
The best solution is such cases (where you are not sending an email invitation to the survey) is to add a question in your survey asking the respondents to enter their email address.
We provide an Export batch for External Distribution option. You can generate a batch for External Distribution and distribute the Survey using your own email program (outlook etc.) to send out email links (invitations) to the survey. The Responses will be tracked and also you will have detailed Statistics for the email addresses.