Duplicate Form Submissions

Hello:

I am trying to implement this plugin for a contest that should restrict the number of entries to one per email address. When testing, I can see that if a duplicate entry is submitted it does not save in the entry list, but the form successfully submits and returns the “success” message.

Is there a way to have the submission be rejected if it is a duplicate?

Example: I submit a duplicate entry, CF7 says “Thank you for your message”, no entry saved.

Target functionality: Submit duplicate entry, CF7 rejects, no entry saved.

Thanks.