Email capture?

Is there a way or third-party widget to capture the emails and other field values before submission for in the card layout? Can I retrieve the details from saved partial submissions for marketing campaigns maybe?

Placing an additional submit button somehwere currently else would submit the whole form.

Unfortunately, it's not possible to capture any information without actually submitting the form, it's needed to submit the information in order to have it stored on your JotForm account. 

Now, there are is a feature that will allow you to save the information before the submission and access the data later on, here are some guides that will help you with that: 

https://www.jotform.com/help/97-How-to-Save-Forms-and-Continue-Later

https://www.jotform.com/help/495-Setting-up-the-Continue-Forms-Later-Feature-in-Card-Forms 

Thanks.