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Not quite sure if I understand your concern correctly.
When you say "opt in", are you referring to sending specific email notifications based on a tick box?
If that's the case, it is possible using the Conditional logic, you can check this guide on how to send notifications based on user inputs: http://www.jotform.com/help/167-How-to-send-to-a-specific-email-address-based-on-a-selection
Let us know if I misunderstood your concern.