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Your LimeSurvey version:  6.2.4+230825
Own server or LimeSurvey hosting: own server
Survey theme/template: fruity thwenty three
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I pls need help on this topic: I just created a open survey an wanted to know if it's possible to collect their email addresses at the end to contact them on their concerns. The issue now is that I cannot find any double opt in solution for contacting them via personalized newsletter afterwards. Is there any plugin or other solution that may help?

I think the double opt-in features, etc. are rather something your newsletter software should take care of (e.g. www.phplist.org/ ).

You might be able to pass the email via end URL to the newsletter system, or via API calls, etc.

Limesurvey is a survey tool, thus doesn't have features like double opt-in, etc.